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root/jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.16 by jsr166, Thu Jul 23 19:44:46 2009 UTC vs.
Revision 1.63 by dl, Fri Aug 13 16:21:23 2010 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import java.util.*;
8	>
9		import java.util.concurrent.*;
10	<	import java.util.concurrent.locks.*;
11	<	import java.util.concurrent.atomic.*;
12	<	import sun.misc.Unsafe;
13	<	import java.lang.reflect.*;
10	>
11	>	import java.util.ArrayList;
12	>	import java.util.Arrays;
13	>	import java.util.Collection;
14	>	import java.util.Collections;
15	>	import java.util.List;
16	>	import java.util.concurrent.locks.LockSupport;
17	>	import java.util.concurrent.locks.ReentrantLock;
18	>	import java.util.concurrent.atomic.AtomicInteger;
19	>	import java.util.concurrent.CountDownLatch;
20
21		/**
22	<	* An {@link ExecutorService} for running {@link ForkJoinTask}s.  A
23	<	* ForkJoinPool provides the entry point for submissions from
24	<	* non-ForkJoinTasks, as well as management and monitoring operations.
25	<	* Normally a single ForkJoinPool is used for a large number of
20	<	* submitted tasks. Otherwise, use would not usually outweigh the
21	<	* construction and bookkeeping overhead of creating a large set of
22	<	* threads.
22	>	* An {@link ExecutorService} for running {@link ForkJoinTask}s.
23	>	* A {@code ForkJoinPool} provides the entry point for submissions
24	>	* from non-{@code ForkJoinTask} clients, as well as management and
25	>	* monitoring operations.
26		*
27	<	* <p>ForkJoinPools differ from other kinds of Executors mainly in
28	<	* that they provide <em>work-stealing</em>: all threads in the pool
29	<	* attempt to find and execute subtasks created by other active tasks
30	<	* (eventually blocking if none exist). This makes them efficient when
31	<	* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
32	<	* as the mixed execution of some plain Runnable- or Callable- based
33	<	* activities along with ForkJoinTasks. When setting
34	<	* {@code setAsyncMode}, a ForkJoinPools may also be appropriate for
35	<	* use with fine-grained tasks that are never joined. Otherwise, other
33	<	* ExecutorService implementations are typically more appropriate
34	<	* choices.
27	>	* <p>A {@code ForkJoinPool} differs from other kinds of {@link
28	>	* ExecutorService} mainly by virtue of employing
29	>	* <em>work-stealing</em>: all threads in the pool attempt to find and
30	>	* execute subtasks created by other active tasks (eventually blocking
31	>	* waiting for work if none exist). This enables efficient processing
32	>	* when most tasks spawn other subtasks (as do most {@code
33	>	* ForkJoinTask}s). When setting <em>asyncMode</em> to true in
34	>	* constructors, {@code ForkJoinPool}s may also be appropriate for use
35	>	* with event-style tasks that are never joined.
36		*
37	<	* <p>A ForkJoinPool may be constructed with a given parallelism level
38	<	* (target pool size), which it attempts to maintain by dynamically
39	<	* adding, suspending, or resuming threads, even if some tasks are
40	<	* waiting to join others. However, no such adjustments are performed
41	<	* in the face of blocked IO or other unmanaged synchronization. The
42	<	* nested {@code ManagedBlocker} interface enables extension of
43	<	* the kinds of synchronization accommodated.  The target parallelism
44	<	* level may also be changed dynamically ({@code setParallelism})
45	<	* and thread construction can be limited using methods
45	<	* {@code setMaximumPoolSize} and/or
46	<	* {@code setMaintainsParallelism}.
37	>	* <p>A {@code ForkJoinPool} is constructed with a given target
38	>	* parallelism level; by default, equal to the number of available
39	>	* processors. The pool attempts to maintain enough active (or
40	>	* available) threads by dynamically adding, suspending, or resuming
41	>	* internal worker threads, even if some tasks are stalled waiting to
42	>	* join others. However, no such adjustments are guaranteed in the
43	>	* face of blocked IO or other unmanaged synchronization. The nested
44	>	* {@link ManagedBlocker} interface enables extension of the kinds of
45	>	* synchronization accommodated.
46		*
47		* <p>In addition to execution and lifecycle control methods, this
48		* class provides status check methods (for example
49	<	* {@code getStealCount}) that are intended to aid in developing,
49	>	* {@link #getStealCount}) that are intended to aid in developing,
50		* tuning, and monitoring fork/join applications. Also, method
51	<	* {@code toString} returns indications of pool state in a
51	>	* {@link #toString} returns indications of pool state in a
52		* convenient form for informal monitoring.
53		*
54	+	* <p> As is the case with other ExecutorServices, there are three
55	+	* main task execution methods summarized in the following
56	+	* table. These are designed to be used by clients not already engaged
57	+	* in fork/join computations in the current pool.  The main forms of
58	+	* these methods accept instances of {@code ForkJoinTask}, but
59	+	* overloaded forms also allow mixed execution of plain {@code
60	+	* Runnable}- or {@code Callable}- based activities as well.  However,
61	+	* tasks that are already executing in a pool should normally
62	+	* <em>NOT</em> use these pool execution methods, but instead use the
63	+	* within-computation forms listed in the table.
64	+	*
65	+	* <table BORDER CELLPADDING=3 CELLSPACING=1>
66	+	*  <tr>
67	+	*    <td></td>
68	+	*    <td ALIGN=CENTER> <b>Call from non-fork/join clients</b></td>
69	+	*    <td ALIGN=CENTER> <b>Call from within fork/join computations</b></td>
70	+	*  </tr>
71	+	*  <tr>
72	+	*    <td> <b>Arange async execution</td>
73	+	*    <td> {@link #execute(ForkJoinTask)}</td>
74	+	*    <td> {@link ForkJoinTask#fork}</td>
75	+	*  </tr>
76	+	*  <tr>
77	+	*    <td> <b>Await and obtain result</td>
78	+	*    <td> {@link #invoke(ForkJoinTask)}</td>
79	+	*    <td> {@link ForkJoinTask#invoke}</td>
80	+	*  </tr>
81	+	*  <tr>
82	+	*    <td> <b>Arrange exec and obtain Future</td>
83	+	*    <td> {@link #submit(ForkJoinTask)}</td>
84	+	*    <td> {@link ForkJoinTask#fork} (ForkJoinTasks <em>are</em> Futures)</td>
85	+	*  </tr>
86	+	* </table>
87	+	*
88	+	* <p><b>Sample Usage.</b> Normally a single {@code ForkJoinPool} is
89	+	* used for all parallel task execution in a program or subsystem.
90	+	* Otherwise, use would not usually outweigh the construction and
91	+	* bookkeeping overhead of creating a large set of threads. For
92	+	* example, a common pool could be used for the {@code SortTasks}
93	+	* illustrated in {@link RecursiveAction}. Because {@code
94	+	* ForkJoinPool} uses threads in {@linkplain java.lang.Thread#isDaemon
95	+	* daemon} mode, there is typically no need to explicitly {@link
96	+	* #shutdown} such a pool upon program exit.
97	+	*
98	+	* <pre>
99	+	* static final ForkJoinPool mainPool = new ForkJoinPool();
100	+	* ...
101	+	* public void sort(long[] array) {
102	+	*   mainPool.invoke(new SortTask(array, 0, array.length));
103	+	* }
104	+	* </pre>
105	+	*
106		* <p><b>Implementation notes</b>: This implementation restricts the
107		* maximum number of running threads to 32767. Attempts to create
108	<	* pools with greater than the maximum result in
109	<	* IllegalArgumentExceptions.
108	>	* pools with greater than the maximum number result in
109	>	* {@code IllegalArgumentException}.
110	>	*
111	>	* <p>This implementation rejects submitted tasks (that is, by throwing
112	>	* {@link RejectedExecutionException}) only when the pool is shut down
113	>	* or internal resources have been exhausted.
114		*
115		* @since 1.7
116		* @author Doug Lea
#	Line 63 | Line 118 | import java.lang.reflect.*;
118		public class ForkJoinPool extends AbstractExecutorService {
119
120		/*
121	<	* See the extended comments interspersed below for design,
122	<	* rationale, and walkthroughs.
123	<	*/
124	<
125	<	/** Mask for packing and unpacking shorts */
126	<	private static final int  shortMask = 0xffff;
127	<
128	<	/** Max pool size -- must be a power of two minus 1 */
129	<	private static final int MAX_THREADS =  0x7FFF;
130	<
131	<	/**
132	<	* Factory for creating new ForkJoinWorkerThreads.  A
133	<	* ForkJoinWorkerThreadFactory must be defined and used for
134	<	* ForkJoinWorkerThread subclasses that extend base functionality
135	<	* or initialize threads with different contexts.
121	>	* Implementation Overview
122	>	*
123	>	* This class provides the central bookkeeping and control for a
124	>	* set of worker threads: Submissions from non-FJ threads enter
125	>	* into a submission queue. Workers take these tasks and typically
126	>	* split them into subtasks that may be stolen by other workers.
127	>	* The main work-stealing mechanics implemented in class
128	>	* ForkJoinWorkerThread give first priority to processing tasks
129	>	* from their own queues (LIFO or FIFO, depending on mode), then
130	>	* to randomized FIFO steals of tasks in other worker queues, and
131	>	* lastly to new submissions. These mechanics do not consider
132	>	* affinities, loads, cache localities, etc, so rarely provide the
133	>	* best possible performance on a given machine, but portably
134	>	* provide good throughput by averaging over these factors.
135	>	* (Further, even if we did try to use such information, we do not
136	>	* usually have a basis for exploiting it. For example, some sets
137	>	* of tasks profit from cache affinities, but others are harmed by
138	>	* cache pollution effects.)
139	>	*
140	>	* Beyond work-stealing support and essential bookkeeping, the
141	>	* main responsibility of this framework is to take actions when
142	>	* one worker is waiting to join a task stolen (or always held by)
143	>	* another.  Becauae we are multiplexing many tasks on to a pool
144	>	* of workers, we can't just let them block (as in Thread.join).
145	>	* We also cannot just reassign the joiner's run-time stack with
146	>	* another and replace it later, which would be a form of
147	>	* "continuation", that even if possible is not necessarily a good
148	>	* idea. Given that the creation costs of most threads on most
149	>	* systems mainly surrounds setting up runtime stacks, thread
150	>	* creation and switching is usually not much more expensive than
151	>	* stack creation and switching, and is more flexible). Instead we
152	>	* combine two tactics:
153	>	*
154	>	*   Helping: Arranging for the joiner to execute some task that it
155	>	*      would be running if the steal had not occurred.  Method
156	>	*      ForkJoinWorkerThread.helpJoinTask tracks joining->stealing
157	>	*      links to try to find such a task.
158	>	*
159	>	*   Compensating: Unless there are already enough live threads,
160	>	*      method helpMaintainParallelism() may create or or
161	>	*      re-activate a spare thread to compensate for blocked
162	>	*      joiners until they unblock.
163	>	*
164	>	* Because the determining existence of conservatively safe
165	>	* helping targets, the availability of already-created spares,
166	>	* and the apparent need to create new spares are all racy and
167	>	* require heuristic guidance, we rely on multiple retries of
168	>	* each. Further, because it is impossible to keep exactly the
169	>	* target (parallelism) number of threads running at any given
170	>	* time, we allow compensation during joins to fail, and enlist
171	>	* all other threads to help out whenever they are not otherwise
172	>	* occupied (i.e., mainly in method preStep).
173	>	*
174	>	* The ManagedBlocker extension API can't use helping so relies
175	>	* only on compensation in method awaitBlocker.
176	>	*
177	>	* The main throughput advantages of work-stealing stem from
178	>	* decentralized control -- workers mostly steal tasks from each
179	>	* other. We do not want to negate this by creating bottlenecks
180	>	* implementing other management responsibilities. So we use a
181	>	* collection of techniques that avoid, reduce, or cope well with
182	>	* contention. These entail several instances of bit-packing into
183	>	* CASable fields to maintain only the minimally required
184	>	* atomicity. To enable such packing, we restrict maximum
185	>	* parallelism to (1<<15)-1 (enabling twice this (to accommodate
186	>	* unbalanced increments and decrements) to fit into a 16 bit
187	>	* field, which is far in excess of normal operating range.  Even
188	>	* though updates to some of these bookkeeping fields do sometimes
189	>	* contend with each other, they don't normally cache-contend with
190	>	* updates to others enough to warrant memory padding or
191	>	* isolation. So they are all held as fields of ForkJoinPool
192	>	* objects.  The main capabilities are as follows:
193	>	*
194	>	* 1. Creating and removing workers. Workers are recorded in the
195	>	* "workers" array. This is an array as opposed to some other data
196	>	* structure to support index-based random steals by workers.
197	>	* Updates to the array recording new workers and unrecording
198	>	* terminated ones are protected from each other by a lock
199	>	* (workerLock) but the array is otherwise concurrently readable,
200	>	* and accessed directly by workers. To simplify index-based
201	>	* operations, the array size is always a power of two, and all
202	>	* readers must tolerate null slots. Currently, all worker thread
203	>	* creation is on-demand, triggered by task submissions,
204	>	* replacement of terminated workers, and/or compensation for
205	>	* blocked workers. However, all other support code is set up to
206	>	* work with other policies.
207	>	*
208	>	* To ensure that we do not hold on to worker references that
209	>	* would prevent GC, ALL accesses to workers are via indices into
210	>	* the workers array (which is one source of some of the unusual
211	>	* code constructions here). In essence, the workers array serves
212	>	* as a WeakReference mechanism. Thus for example the event queue
213	>	* stores worker indices, not worker references. Access to the
214	>	* workers in associated methods (for example releaseEventWaiters)
215	>	* must both index-check and null-check the IDs. All such accesses
216	>	* ignore bad IDs by returning out early from what they are doing,
217	>	* since this can only be associated with shutdown, in which case
218	>	* it is OK to give up. On termination, we just clobber these
219	>	* data structures without trying to use them.
220	>	*
221	>	* 2. Bookkeeping for dynamically adding and removing workers. We
222	>	* aim to approximately maintain the given level of parallelism.
223	>	* When some workers are known to be blocked (on joins or via
224	>	* ManagedBlocker), we may create or resume others to take their
225	>	* place until they unblock (see below). Implementing this
226	>	* requires counts of the number of "running" threads (i.e., those
227	>	* that are neither blocked nor artifically suspended) as well as
228	>	* the total number.  These two values are packed into one field,
229	>	* "workerCounts" because we need accurate snapshots when deciding
230	>	* to create, resume or suspend.  Note however that the
231	>	* correspondance of these counts to reality is not guaranteed. In
232	>	* particular updates for unblocked threads may lag until they
233	>	* actually wake up.
234	>	*
235	>	* 3. Maintaining global run state. The run state of the pool
236	>	* consists of a runLevel (SHUTDOWN, TERMINATING, etc) similar to
237	>	* those in other Executor implementations, as well as a count of
238	>	* "active" workers -- those that are, or soon will be, or
239	>	* recently were executing tasks. The runLevel and active count
240	>	* are packed together in order to correctly trigger shutdown and
241	>	* termination. Without care, active counts can be subject to very
242	>	* high contention.  We substantially reduce this contention by
243	>	* relaxing update rules.  A worker must claim active status
244	>	* prospectively, by activating if it sees that a submitted or
245	>	* stealable task exists (it may find after activating that the
246	>	* task no longer exists). It stays active while processing this
247	>	* task (if it exists) and any other local subtasks it produces,
248	>	* until it cannot find any other tasks. It then tries
249	>	* inactivating (see method preStep), but upon update contention
250	>	* instead scans for more tasks, later retrying inactivation if it
251	>	* doesn't find any.
252	>	*
253	>	* 4. Managing idle workers waiting for tasks. We cannot let
254	>	* workers spin indefinitely scanning for tasks when none are
255	>	* available. On the other hand, we must quickly prod them into
256	>	* action when new tasks are submitted or generated.  We
257	>	* park/unpark these idle workers using an event-count scheme.
258	>	* Field eventCount is incremented upon events that may enable
259	>	* workers that previously could not find a task to now find one:
260	>	* Submission of a new task to the pool, or another worker pushing
261	>	* a task onto a previously empty queue.  (We also use this
262	>	* mechanism for termination actions that require wakeups of idle
263	>	* workers).  Each worker maintains its last known event count,
264	>	* and blocks when a scan for work did not find a task AND its
265	>	* lastEventCount matches the current eventCount. Waiting idle
266	>	* workers are recorded in a variant of Treiber stack headed by
267	>	* field eventWaiters which, when nonzero, encodes the thread
268	>	* index and count awaited for by the worker thread most recently
269	>	* calling eventSync. This thread in turn has a record (field
270	>	* nextEventWaiter) for the next waiting worker.  In addition to
271	>	* allowing simpler decisions about need for wakeup, the event
272	>	* count bits in eventWaiters serve the role of tags to avoid ABA
273	>	* errors in Treiber stacks.  To reduce delays in task diffusion,
274	>	* workers not otherwise occupied may invoke method
275	>	* releaseEventWaiters, that removes and signals (unparks) workers
276	>	* not waiting on current count. To reduce stalls, To minimize
277	>	* task production stalls associate with signalling, any worker
278	>	* pushing a task on an empty queue invokes the weaker method
279	>	* signalWork, that only releases idle workers until it detects
280	>	* interference by other threads trying to release, and lets them
281	>	* take over.  The net effect is a tree-like diffusion of signals,
282	>	* where released threads (and possibly others) help with unparks.
283	>	* To further reduce contention effects a bit, failed CASes to
284	>	* increment field eventCount are tolerated without retries.
285	>	* Conceptually they are merged into the same event, which is OK
286	>	* when their only purpose is to enable workers to scan for work.
287	>	*
288	>	* 5. Managing suspension of extra workers. When a worker is about
289	>	* to block waiting for a join (or via ManagedBlockers), we may
290	>	* create a new thread to maintain parallelism level, or at least
291	>	* avoid starvation. Usually, extra threads are needed for only
292	>	* very short periods, yet join dependencies are such that we
293	>	* sometimes need them in bursts. Rather than create new threads
294	>	* each time this happens, we suspend no-longer-needed extra ones
295	>	* as "spares". For most purposes, we don't distinguish "extra"
296	>	* spare threads from normal "core" threads: On each call to
297	>	* preStep (the only point at which we can do this) a worker
298	>	* checks to see if there are now too many running workers, and if
299	>	* so, suspends itself.  Method helpMaintainParallelism looks for
300	>	* suspended threads to resume before considering creating a new
301	>	* replacement. The spares themselves are encoded on another
302	>	* variant of a Treiber Stack, headed at field "spareWaiters".
303	>	* Note that the use of spares is intrinsically racy.  One thread
304	>	* may become a spare at about the same time as another is
305	>	* needlessly being created. We counteract this and related slop
306	>	* in part by requiring resumed spares to immediately recheck (in
307	>	* preStep) to see whether they they should re-suspend.  To avoid
308	>	* long-term build-up of spares, the oldest spare (see
309	>	* ForkJoinWorkerThread.suspendAsSpare) occasionally wakes up if
310	>	* not signalled and calls tryTrimSpare, which uses two different
311	>	* thresholds: Always killing if the number of spares is greater
312	>	* that 25% of total, and killing others only at a slower rate
313	>	* (UNUSED_SPARE_TRIM_RATE_NANOS).
314	>	*
315	>	* 6. Deciding when to create new workers. The main dynamic
316	>	* control in this class is deciding when to create extra threads
317	>	* in method helpMaintainParallelism. We would like to keep
318	>	* exactly #parallelism threads running, which is an impossble
319	>	* task. We always need to create one when the number of running
320	>	* threads would become zero and all workers are busy. Beyond
321	>	* this, we must rely on heuristics that work well in the the
322	>	* presence of transients phenomena such as GC stalls, dynamic
323	>	* compilation, and wake-up lags. These transients are extremely
324	>	* common -- we are normally trying to fully saturate the CPUs on
325	>	* a machine, so almost any activity other than running tasks
326	>	* impedes accuracy. Our main defense is to allow some slack in
327	>	* creation thresholds, using rules that reflect the fact that the
328	>	* more threads we have running, the more likely that we are
329	>	* underestimating the number running threads. The rules also
330	>	* better cope with the fact that some of the methods in this
331	>	* class tend to never become compiled (but are interpreted), so
332	>	* some components of the entire set of controls might execute 100
333	>	* times faster than others. And similarly for cases where the
334	>	* apparent lack of work is just due to GC stalls and other
335	>	* transient system activity.
336	>	*
337	>	* Beware that there is a lot of representation-level coupling
338	>	* among classes ForkJoinPool, ForkJoinWorkerThread, and
339	>	* ForkJoinTask.  For example, direct access to "workers" array by
340	>	* workers, and direct access to ForkJoinTask.status by both
341	>	* ForkJoinPool and ForkJoinWorkerThread.  There is little point
342	>	* trying to reduce this, since any associated future changes in
343	>	* representations will need to be accompanied by algorithmic
344	>	* changes anyway.
345	>	*
346	>	* Style notes: There are lots of inline assignments (of form
347	>	* "while ((local = field) != 0)") which are usually the simplest
348	>	* way to ensure the required read orderings (which are sometimes
349	>	* critical). Also several occurrences of the unusual "do {}
350	>	* while(!cas...)" which is the simplest way to force an update of
351	>	* a CAS'ed variable. There are also other coding oddities that
352	>	* help some methods perform reasonably even when interpreted (not
353	>	* compiled), at the expense of some messy constructions that
354	>	* reduce byte code counts.
355	>	*
356	>	* The order of declarations in this file is: (1) statics (2)
357	>	* fields (along with constants used when unpacking some of them)
358	>	* (3) internal control methods (4) callbacks and other support
359	>	* for ForkJoinTask and ForkJoinWorkerThread classes, (5) exported
360	>	* methods (plus a few little helpers).
361	>	*/
362	>
363	>	/**
364	>	* Factory for creating new {@link ForkJoinWorkerThread}s.
365	>	* A {@code ForkJoinWorkerThreadFactory} must be defined and used
366	>	* for {@code ForkJoinWorkerThread} subclasses that extend base
367	>	* functionality or initialize threads with different contexts.
368		*/
369		public static interface ForkJoinWorkerThreadFactory {
370		/**
371		* Returns a new worker thread operating in the given pool.
372		*
373		* @param pool the pool this thread works in
374	<	* @throws NullPointerException if pool is null
374	>	* @throws NullPointerException if the pool is null
375		*/
376		public ForkJoinWorkerThread newThread(ForkJoinPool pool);
377		}
378
379		/**
380	<	* Default ForkJoinWorkerThreadFactory implementation, creates a
380	>	* Default ForkJoinWorkerThreadFactory implementation; creates a
381		* new ForkJoinWorkerThread.
382		*/
383	<	static class  DefaultForkJoinWorkerThreadFactory
383	>	static class DefaultForkJoinWorkerThreadFactory
384		implements ForkJoinWorkerThreadFactory {
385		public ForkJoinWorkerThread newThread(ForkJoinPool pool) {
386	<	try {
100	<	return new ForkJoinWorkerThread(pool);
101	<	} catch (OutOfMemoryError oom)  {
102	<	return null;
103	<	}
386	>	return new ForkJoinWorkerThread(pool);
387		}
388		}
389
#	Line 136 | Line 419 | public class ForkJoinPool extends Abstra
419		new AtomicInteger();
420
421		/**
422	<	* Array holding all worker threads in the pool. Initialized upon
423	<	* first use. Array size must be a power of two.  Updates and
424	<	* replacements are protected by workerLock, but it is always kept
425	<	* in a consistent enough state to be randomly accessed without
426	<	* locking by workers performing work-stealing.
422	>	* Absolute bound for parallelism level. Twice this number plus
423	>	* one (i.e., 0xfff) must fit into a 16bit field to enable
424	>	* word-packing for some counts and indices.
425	>	*/
426	>	private static final int MAX_WORKERS   = 0x7fff;
427	>
428	>	/**
429	>	* Array holding all worker threads in the pool.  Array size must
430	>	* be a power of two.  Updates and replacements are protected by
431	>	* workerLock, but the array is always kept in a consistent enough
432	>	* state to be randomly accessed without locking by workers
433	>	* performing work-stealing, as well as other traversal-based
434	>	* methods in this class. All readers must tolerate that some
435	>	* array slots may be null.
436		*/
437		volatile ForkJoinWorkerThread[] workers;
438
439		/**
440	<	* Lock protecting access to workers.
440	>	* Queue for external submissions.
441		*/
442	<	private final ReentrantLock workerLock;
442	>	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
443
444		/**
445	<	* Condition for awaitTermination.
445	>	* Lock protecting updates to workers array.
446		*/
447	<	private final Condition termination;
447	>	private final ReentrantLock workerLock;
448
449		/**
450	<	* The uncaught exception handler used when any worker
159	<	* abruptly terminates
450	>	* Latch released upon termination.
451		*/
452	<	private Thread.UncaughtExceptionHandler ueh;
452	>	private final Phaser termination;
453
454		/**
455		* Creation factory for worker threads.
#	Line 166 | Line 457 | public class ForkJoinPool extends Abstra
457		private final ForkJoinWorkerThreadFactory factory;
458
459		/**
169	–	* Head of stack of threads that were created to maintain
170	–	* parallelism when other threads blocked, but have since
171	–	* suspended when the parallelism level rose.
172	–	*/
173	–	private volatile WaitQueueNode spareStack;
174	–
175	–	/**
460		* Sum of per-thread steal counts, updated only when threads are
461		* idle or terminating.
462		*/
463	<	private final AtomicLong stealCount;
463	>	private volatile long stealCount;
464
465		/**
466	<	* Queue for external submissions.
466	>	* The last nanoTime that a spare thread was trimmed
467		*/
468	<	private final LinkedTransferQueue<ForkJoinTask<?>> submissionQueue;
468	>	private volatile long trimTime;
469
470		/**
471	<	* Head of Treiber stack for barrier sync. See below for explanation
471	>	* The rate at which to trim unused spares
472		*/
473	<	private volatile WaitQueueNode syncStack;
473	>	static final long UNUSED_SPARE_TRIM_RATE_NANOS =
474	>	1000L * 1000L * 1000L; // 1 sec
475
476		/**
477	<	* The count for event barrier
477	>	* Encoded record of top of treiber stack of threads waiting for
478	>	* events. The top 32 bits contain the count being waited for. The
479	>	* bottom 16 bits contains one plus the pool index of waiting
480	>	* worker thread. (Bits 16-31 are unused.)
481		*/
482	<	private volatile long eventCount;
482	>	private volatile long eventWaiters;
483	>
484	>	private static final int  EVENT_COUNT_SHIFT = 32;
485	>	private static final long WAITER_ID_MASK    = (1L << 16) - 1L;
486
487		/**
488	<	* Pool number, just for assigning useful names to worker threads
488	>	* A counter for events that may wake up worker threads:
489	>	*   - Submission of a new task to the pool
490	>	*   - A worker pushing a task on an empty queue
491	>	*   - termination
492		*/
493	<	private final int poolNumber;
493	>	private volatile int eventCount;
494	>
495	>	/**
496	>	* Encoded record of top of treiber stack of spare threads waiting
497	>	* for resumption. The top 16 bits contain an arbitrary count to
498	>	* avoid ABA effects. The bottom 16bits contains one plus the pool
499	>	* index of waiting worker thread.
500	>	*/
501	>	private volatile int spareWaiters;
502	>
503	>	private static final int SPARE_COUNT_SHIFT = 16;
504	>	private static final int SPARE_ID_MASK     = (1 << 16) - 1;
505	>
506	>	/**
507	>	* Lifecycle control. The low word contains the number of workers
508	>	* that are (probably) executing tasks. This value is atomically
509	>	* incremented before a worker gets a task to run, and decremented
510	>	* when worker has no tasks and cannot find any.  Bits 16-18
511	>	* contain runLevel value. When all are zero, the pool is
512	>	* running. Level transitions are monotonic (running -> shutdown
513	>	* -> terminating -> terminated) so each transition adds a bit.
514	>	* These are bundled together to ensure consistent read for
515	>	* termination checks (i.e., that runLevel is at least SHUTDOWN
516	>	* and active threads is zero).
517	>	*/
518	>	private volatile int runState;
519	>
520	>	// Note: The order among run level values matters.
521	>	private static final int RUNLEVEL_SHIFT     = 16;
522	>	private static final int SHUTDOWN           = 1 << RUNLEVEL_SHIFT;
523	>	private static final int TERMINATING        = 1 << (RUNLEVEL_SHIFT + 1);
524	>	private static final int TERMINATED         = 1 << (RUNLEVEL_SHIFT + 2);
525	>	private static final int ACTIVE_COUNT_MASK  = (1 << RUNLEVEL_SHIFT) - 1;
526	>	private static final int ONE_ACTIVE         = 1; // active update delta
527
528		/**
529	<	* The maximum allowed pool size
529	>	* Holds number of total (i.e., created and not yet terminated)
530	>	* and running (i.e., not blocked on joins or other managed sync)
531	>	* threads, packed together to ensure consistent snapshot when
532	>	* making decisions about creating and suspending spare
533	>	* threads. Updated only by CAS. Note that adding a new worker
534	>	* requires incrementing both counts, since workers start off in
535	>	* running state.
536		*/
537	<	private volatile int maxPoolSize;
537	>	private volatile int workerCounts;
538	>
539	>	private static final int TOTAL_COUNT_SHIFT  = 16;
540	>	private static final int RUNNING_COUNT_MASK = (1 << TOTAL_COUNT_SHIFT) - 1;
541	>	private static final int ONE_RUNNING        = 1;
542	>	private static final int ONE_TOTAL          = 1 << TOTAL_COUNT_SHIFT;
543
544		/**
545	<	* The desired parallelism level, updated only under workerLock.
545	>	* The target parallelism level.
546	>	* Accessed directly by ForkJoinWorkerThreads.
547		*/
548	<	private volatile int parallelism;
548	>	final int parallelism;
549
550		/**
551		* True if use local fifo, not default lifo, for local polling
552	+	* Read by, and replicated by ForkJoinWorkerThreads
553		*/
554	<	private volatile boolean locallyFifo;
554	>	final boolean locallyFifo;
555
556		/**
557	<	* Holds number of total (i.e., created and not yet terminated)
558	<	* and running (i.e., not blocked on joins or other managed sync)
219	<	* threads, packed into one int to ensure consistent snapshot when
220	<	* making decisions about creating and suspending spare
221	<	* threads. Updated only by CAS.  Note: CASes in
222	<	* updateRunningCount and preJoin assume that running active count
223	<	* is in low word, so need to be modified if this changes.
557	>	* The uncaught exception handler used when any worker abruptly
558	>	* terminates.
559		*/
560	<	private volatile int workerCounts;
560	>	private final Thread.UncaughtExceptionHandler ueh;
561	>
562	>	/**
563	>	* Pool number, just for assigning useful names to worker threads
564	>	*/
565	>	private final int poolNumber;
566	>
567
568	<	private static int totalCountOf(int s)           { return s >>> 16;  }
569	<	private static int runningCountOf(int s)         { return s & shortMask; }
229	<	private static int workerCountsFor(int t, int r) { return (t << 16) + r; }
568	>	// Utilities for CASing fields. Note that several of these
569	>	// are manually inlined by callers
570
571		/**
572	<	* Adds delta (which may be negative) to running count.  This must
233	<	* be called before (with negative arg) and after (with positive)
234	<	* any managed synchronization (i.e., mainly, joins).
235	<	* @param delta the number to add
572	>	* Increments running count part of workerCounts
573		*/
574	<	final void updateRunningCount(int delta) {
575	<	int s;
576	<	do;while (!casWorkerCounts(s = workerCounts, s + delta));
574	>	final void incrementRunningCount() {
575	>	int c;
576	>	do {} while (!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
577	>	c = workerCounts,
578	>	c + ONE_RUNNING));
579		}
580
581		/**
582	<	* Adds delta (which may be negative) to both total and running
244	<	* count.  This must be called upon creation and termination of
245	<	* worker threads.
246	<	* @param delta the number to add
582	>	* Tries to decrement running count unless already zero
583		*/
584	<	private void updateWorkerCount(int delta) {
585	<	int d = delta + (delta << 16); // add to both lo and hi parts
586	<	int s;
587	<	do;while (!casWorkerCounts(s = workerCounts, s + d));
584	>	final boolean tryDecrementRunningCount() {
585	>	int wc = workerCounts;
586	>	if ((wc & RUNNING_COUNT_MASK) == 0)
587	>	return false;
588	>	return UNSAFE.compareAndSwapInt(this, workerCountsOffset,
589	>	wc, wc - ONE_RUNNING);
590		}
591
592		/**
593	<	* Lifecycle control. High word contains runState, low word
594	<	* contains the number of workers that are (probably) executing
595	<	* tasks. This value is atomically incremented before a worker
596	<	* gets a task to run, and decremented when worker has no tasks
597	<	* and cannot find any. These two fields are bundled together to
260	<	* support correct termination triggering.  Note: activeCount
261	<	* CAS'es cheat by assuming active count is in low word, so need
262	<	* to be modified if this changes
593	>	* Forces decrement of encoded workerCounts, awaiting nonzero if
594	>	* (rarely) necessary when other count updates lag.
595	>	*
596	>	* @param dr -- either zero or ONE_RUNNING
597	>	* @param dt == either zero or ONE_TOTAL
598		*/
599	<	private volatile int runControl;
600	<
601	<	// RunState values. Order among values matters
602	<	private static final int RUNNING     = 0;
603	<	private static final int SHUTDOWN    = 1;
604	<	private static final int TERMINATING = 2;
605	<	private static final int TERMINATED  = 3;
599	>	private void decrementWorkerCounts(int dr, int dt) {
600	>	for (;;) {
601	>	int wc = workerCounts;
602	>	if (wc == 0 && (runState & TERMINATED) != 0)
603	>	return; // lagging termination on a backout
604	>	if ((wc & RUNNING_COUNT_MASK)  - dr < 0 ||
605	>	(wc >>> TOTAL_COUNT_SHIFT) - dt < 0)
606	>	Thread.yield();
607	>	if (UNSAFE.compareAndSwapInt(this, workerCountsOffset,
608	>	wc, wc - (dr + dt)))
609	>	return;
610	>	}
611	>	}
612
613	<	private static int runStateOf(int c)             { return c >>> 16; }
614	<	private static int activeCountOf(int c)          { return c & shortMask; }
615	<	private static int runControlFor(int r, int a)   { return (r << 16) + a; }
613	>	/**
614	>	* Increments event count
615	>	*/
616	>	private void advanceEventCount() {
617	>	int c;
618	>	do {} while(!UNSAFE.compareAndSwapInt(this, eventCountOffset,
619	>	c = eventCount, c+1));
620	>	}
621
622		/**
623	<	* Try incrementing active count; fail on contention. Called by
624	<	* workers before/during executing tasks.
623	>	* Tries incrementing active count; fails on contention.
624	>	* Called by workers before executing tasks.
625	>	*
626		* @return true on success
627		*/
628		final boolean tryIncrementActiveCount() {
629	<	int c = runControl;
630	<	return casRunControl(c, c+1);
629	>	int c;
630	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
631	>	c = runState, c + ONE_ACTIVE);
632		}
633
634		/**
635		* Tries decrementing active count; fails on contention.
636	<	* Possibly triggers termination on success.
289	<	* Called by workers when they can't find tasks.
290	<	* @return true on success
636	>	* Called when workers cannot find tasks to run.
637		*/
638		final boolean tryDecrementActiveCount() {
639	<	int c = runControl;
640	<	int nextc = c - 1;
641	<	if (!casRunControl(c, nextc))
296	<	return false;
297	<	if (canTerminateOnShutdown(nextc))
298	<	terminateOnShutdown();
299	<	return true;
639	>	int c;
640	>	return UNSAFE.compareAndSwapInt(this, runStateOffset,
641	>	c = runState, c - ONE_ACTIVE);
642		}
643
644		/**
645	<	* Returns true if argument represents zero active count and
646	<	* nonzero runstate, which is the triggering condition for
305	<	* terminating on shutdown.
645	>	* Advances to at least the given level. Returns true if not
646	>	* already in at least the given level.
647		*/
648	<	private static boolean canTerminateOnShutdown(int c) {
649	<	return ((c & -c) >>> 16) != 0; // i.e. least bit is nonzero runState bit
648	>	private boolean advanceRunLevel(int level) {
649	>	for (;;) {
650	>	int s = runState;
651	>	if ((s & level) != 0)
652	>	return false;
653	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset, s, s | level))
654	>	return true;
655	>	}
656		}
657
658	+	// workers array maintenance
659	+
660		/**
661	<	* Transition run state to at least the given state. Return true
313	<	* if not already at least given state.
661	>	* Records and returns a workers array index for new worker.
662		*/
663	<	private boolean transitionRunStateTo(int state) {
664	<	for (;;) {
665	<	int c = runControl;
666	<	if (runStateOf(c) >= state)
667	<	return false;
668	<	if (casRunControl(c, runControlFor(state, activeCountOf(c))))
669	<	return true;
663	>	private int recordWorker(ForkJoinWorkerThread w) {
664	>	// Try using slot totalCount-1. If not available, scan and/or resize
665	>	int k = (workerCounts >>> TOTAL_COUNT_SHIFT) - 1;
666	>	final ReentrantLock lock = this.workerLock;
667	>	lock.lock();
668	>	try {
669	>	ForkJoinWorkerThread[] ws = workers;
670	>	int n = ws.length;
671	>	if (k < 0 || k >= n || ws[k] != null) {
672	>	for (k = 0; k < n && ws[k] != null; ++k)
673	>	;
674	>	if (k == n)
675	>	ws = Arrays.copyOf(ws, n << 1);
676	>	}
677	>	ws[k] = w;
678	>	workers = ws; // volatile array write ensures slot visibility
679	>	} finally {
680	>	lock.unlock();
681		}
682	+	return k;
683		}
684
685		/**
686	<	* Controls whether to add spares to maintain parallelism
686	>	* Nulls out record of worker in workers array
687		*/
688	<	private volatile boolean maintainsParallelism;
688	>	private void forgetWorker(ForkJoinWorkerThread w) {
689	>	int idx = w.poolIndex;
690	>	// Locking helps method recordWorker avoid unecessary expansion
691	>	final ReentrantLock lock = this.workerLock;
692	>	lock.lock();
693	>	try {
694	>	ForkJoinWorkerThread[] ws = workers;
695	>	if (idx >= 0 && idx < ws.length && ws[idx] == w) // verify
696	>	ws[idx] = null;
697	>	} finally {
698	>	lock.unlock();
699	>	}
700	>	}
701
702	<	// Constructors
702	>	// adding and removing workers
703
704		/**
705	<	* Creates a ForkJoinPool with a pool size equal to the number of
706	<	* processors available on the system and using the default
707	<	* ForkJoinWorkerThreadFactory,
336	<	* @throws SecurityException if a security manager exists and
337	<	*         the caller is not permitted to modify threads
338	<	*         because it does not hold {@link
339	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
705	>	* Tries to create and add new worker. Assumes that worker counts
706	>	* are already updated to accommodate the worker, so adjusts on
707	>	* failure.
708		*/
709	<	public ForkJoinPool() {
710	<	this(Runtime.getRuntime().availableProcessors(),
711	<	defaultForkJoinWorkerThreadFactory);
709	>	private void addWorker() {
710	>	ForkJoinWorkerThread w = null;
711	>	try {
712	>	w = factory.newThread(this);
713	>	} finally { // Adjust on either null or exceptional factory return
714	>	if (w == null) {
715	>	decrementWorkerCounts(ONE_RUNNING, ONE_TOTAL);
716	>	tryTerminate(false); // in case of failure during shutdown
717	>	}
718	>	}
719	>	if (w != null)
720	>	w.start(recordWorker(w), ueh);
721		}
722
723		/**
724	<	* Creates a ForkJoinPool with the indicated parallelism level
725	<	* threads, and using the default ForkJoinWorkerThreadFactory,
726	<	* @param parallelism the number of worker threads
727	<	* @throws IllegalArgumentException if parallelism less than or
728	<	* equal to zero
352	<	* @throws SecurityException if a security manager exists and
353	<	*         the caller is not permitted to modify threads
354	<	*         because it does not hold {@link
355	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
724	>	* Final callback from terminating worker.  Removes record of
725	>	* worker from array, and adjusts counts. If pool is shutting
726	>	* down, tries to complete terminatation.
727	>	*
728	>	* @param w the worker
729		*/
730	<	public ForkJoinPool(int parallelism) {
731	<	this(parallelism, defaultForkJoinWorkerThreadFactory);
730	>	final void workerTerminated(ForkJoinWorkerThread w) {
731	>	forgetWorker(w);
732	>	decrementWorkerCounts(w.isTrimmed()? 0 : ONE_RUNNING, ONE_TOTAL);
733	>	while (w.stealCount != 0) // collect final count
734	>	tryAccumulateStealCount(w);
735	>	tryTerminate(false);
736		}
737
738	+	// Waiting for and signalling events
739	+
740		/**
741	<	* Creates a ForkJoinPool with parallelism equal to the number of
742	<	* processors available on the system and using the given
743	<	* ForkJoinWorkerThreadFactory,
744	<	* @param factory the factory for creating new threads
745	<	* @throws NullPointerException if factory is null
746	<	* @throws SecurityException if a security manager exists and
747	<	*         the caller is not permitted to modify threads
369	<	*         because it does not hold {@link
370	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
741	>	* Releases workers blocked on a count not equal to current count.
742	>	* Normally called after precheck that eventWaiters isn't zero to
743	>	* avoid wasted array checks.
744	>	*
745	>	* @param signalling true if caller is a signalling worker so can
746	>	* exit upon (conservatively) detected contention by other threads
747	>	* who will continue to release
748		*/
749	<	public ForkJoinPool(ForkJoinWorkerThreadFactory factory) {
750	<	this(Runtime.getRuntime().availableProcessors(), factory);
749	>	private void releaseEventWaiters(boolean signalling) {
750	>	ForkJoinWorkerThread[] ws = workers;
751	>	int n = ws.length;
752	>	long h; // head of stack
753	>	ForkJoinWorkerThread w; int id, ec;
754	>	while ((id = ((int)((h = eventWaiters) & WAITER_ID_MASK)) - 1) >= 0 &&
755	>	(int)(h >>> EVENT_COUNT_SHIFT) != (ec = eventCount) &&
756	>	id < n && (w = ws[id]) != null) {
757	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
758	>	h, h = w.nextWaiter))
759	>	LockSupport.unpark(w);
760	>	if (signalling && (eventCount != ec || eventWaiters != h))
761	>	break;
762	>	}
763		}
764
765		/**
766	<	* Creates a ForkJoinPool with the given parallelism and factory.
767	<	*
379	<	* @param parallelism the targeted number of worker threads
380	<	* @param factory the factory for creating new threads
381	<	* @throws IllegalArgumentException if parallelism less than or
382	<	* equal to zero, or greater than implementation limit
383	<	* @throws NullPointerException if factory is null
384	<	* @throws SecurityException if a security manager exists and
385	<	*         the caller is not permitted to modify threads
386	<	*         because it does not hold {@link
387	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
766	>	* Tries to advance eventCount and releases waiters. Called only
767	>	* from workers.
768		*/
769	<	public ForkJoinPool(int parallelism, ForkJoinWorkerThreadFactory factory) {
770	<	if (parallelism <= 0 || parallelism > MAX_THREADS)
771	<	throw new IllegalArgumentException();
772	<	if (factory == null)
773	<	throw new NullPointerException();
394	<	checkPermission();
395	<	this.factory = factory;
396	<	this.parallelism = parallelism;
397	<	this.maxPoolSize = MAX_THREADS;
398	<	this.maintainsParallelism = true;
399	<	this.poolNumber = poolNumberGenerator.incrementAndGet();
400	<	this.workerLock = new ReentrantLock();
401	<	this.termination = workerLock.newCondition();
402	<	this.stealCount = new AtomicLong();
403	<	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
404	<	// worker array and workers are lazily constructed
769	>	final void signalWork() {
770	>	int c; // try to increment event count -- CAS failure OK
771	>	UNSAFE.compareAndSwapInt(this, eventCountOffset, c = eventCount, c+1);
772	>	if (eventWaiters != 0L)
773	>	releaseEventWaiters(true);
774		}
775
776		/**
777	<	* Create new worker using factory.
778	<	* @param index the index to assign worker
779	<	* @return new worker, or null of factory failed
777	>	* Blocks worker until terminating or event count
778	>	* advances from last value held by worker
779	>	*
780	>	* @param w the calling worker thread
781		*/
782	<	private ForkJoinWorkerThread createWorker(int index) {
783	<	Thread.UncaughtExceptionHandler h = ueh;
784	<	ForkJoinWorkerThread w = factory.newThread(this);
785	<	if (w != null) {
786	<	w.poolIndex = index;
787	<	w.setDaemon(true);
788	<	w.setAsyncMode(locallyFifo);
789	<	w.setName("ForkJoinPool-" + poolNumber + "-worker-" + index);
790	<	if (h != null)
791	<	w.setUncaughtExceptionHandler(h);
782	>	private void eventSync(ForkJoinWorkerThread w) {
783	>	int wec = w.lastEventCount;
784	>	long nh = (((long)wec) << EVENT_COUNT_SHIFT) | ((long)(w.poolIndex+1));
785	>	long h;
786	>	while ((runState < SHUTDOWN || !tryTerminate(false)) &&
787	>	((h = eventWaiters) == 0L ||
788	>	(int)(h >>> EVENT_COUNT_SHIFT) == wec) &&
789	>	eventCount == wec) {
790	>	if (UNSAFE.compareAndSwapLong(this, eventWaitersOffset,
791	>	w.nextWaiter = h, nh)) {
792	>	while (runState < TERMINATING && eventCount == wec) {
793	>	if (!tryAccumulateStealCount(w))  // transfer while idle
794	>	continue;
795	>	Thread.interrupted();             // clear/ignore interrupt
796	>	if (eventCount != wec)
797	>	break;
798	>	LockSupport.park(w);
799	>	}
800	>	break;
801	>	}
802		}
803	<	return w;
803	>	w.lastEventCount = eventCount;
804		}
805
806	+	// Maintaining spares
807	+
808		/**
809	<	* Returns a good size for worker array given pool size.
428	<	* Currently requires size to be a power of two.
809	>	* Pushes worker onto the spare stack
810		*/
811	<	private static int arraySizeFor(int ps) {
812	<	return ps <= 1? 1 : (1 << (32 - Integer.numberOfLeadingZeros(ps-1)));
811	>	final void pushSpare(ForkJoinWorkerThread w) {
812	>	int ns = (++w.spareCount << SPARE_COUNT_SHIFT) | (w.poolIndex+1);
813	>	do {} while (!UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
814	>	w.nextSpare = spareWaiters,ns));
815		}
816
817		/**
818	<	* Creates or resizes array if necessary to hold newLength.
819	<	* Call only under exclusion.
437	<	*
438	<	* @return the array
818	>	* Tries (once) to resume a spare if running count is less than
819	>	* target parallelism. Fails on contention or stale workers.
820		*/
821	<	private ForkJoinWorkerThread[] ensureWorkerArrayCapacity(int newLength) {
822	<	ForkJoinWorkerThread[] ws = workers;
823	<	if (ws == null)
824	<	return workers = new ForkJoinWorkerThread[arraySizeFor(newLength)];
825	<	else if (newLength > ws.length)
826	<	return workers = Arrays.copyOf(ws, arraySizeFor(newLength));
827	<	else
828	<	return ws;
821	>	private void tryResumeSpare() {
822	>	int sw, id;
823	>	ForkJoinWorkerThread w;
824	>	ForkJoinWorkerThread[] ws;
825	>	if ((id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
826	>	id < (ws = workers).length && (w = ws[id]) != null &&
827	>	(workerCounts & RUNNING_COUNT_MASK) < parallelism &&
828	>	eventWaiters == 0L &&
829	>	spareWaiters == sw &&
830	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
831	>	sw, w.nextSpare) &&
832	>	w.tryUnsuspend()) {
833	>	int c; // try increment; if contended, finish after unpark
834	>	boolean inc = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
835	>	c = workerCounts,
836	>	c + ONE_RUNNING);
837	>	LockSupport.unpark(w);
838	>	if (!inc) {
839	>	do {} while(!UNSAFE.compareAndSwapInt(this, workerCountsOffset,
840	>	c = workerCounts,
841	>	c + ONE_RUNNING));
842	>	}
843	>	}
844		}
845
846		/**
847	<	* Try to shrink workers into smaller array after one or more terminate
847	>	* Callback from oldest spare occasionally waking up.  Tries
848	>	* (once) to shutdown a spare if more than 25% spare overage, or
849	>	* if UNUSED_SPARE_TRIM_RATE_NANOS have elapsed and there are at
850	>	* least #parallelism running threads. Note that we don't need CAS
851	>	* or locks here because the method is called only from the oldest
852	>	* suspended spare occasionally waking (and even misfires are OK).
853	>	*
854	>	* @param now the wake up nanoTime of caller
855		*/
856	<	private void tryShrinkWorkerArray() {
857	<	ForkJoinWorkerThread[] ws = workers;
858	<	if (ws != null) {
859	<	int len = ws.length;
860	<	int last = len - 1;
861	<	while (last >= 0 && ws[last] == null)
862	<	--last;
863	<	int newLength = arraySizeFor(last+1);
864	<	if (newLength < len)
865	<	workers = Arrays.copyOf(ws, newLength);
856	>	final void tryTrimSpare(long now) {
857	>	long lastTrim = trimTime;
858	>	trimTime = now;
859	>	helpMaintainParallelism(); // first, help wake up any needed spares
860	>	int sw, id;
861	>	ForkJoinWorkerThread w;
862	>	ForkJoinWorkerThread[] ws;
863	>	int pc = parallelism;
864	>	int wc = workerCounts;
865	>	if ((wc & RUNNING_COUNT_MASK) >= pc &&
866	>	(((wc >>> TOTAL_COUNT_SHIFT) - pc) > (pc >>> 2) + 1 ||// approx 25%
867	>	now - lastTrim >= UNUSED_SPARE_TRIM_RATE_NANOS) &&
868	>	(id = ((sw = spareWaiters) & SPARE_ID_MASK) - 1) >= 0 &&
869	>	id < (ws = workers).length && (w = ws[id]) != null &&
870	>	UNSAFE.compareAndSwapInt(this, spareWaitersOffset,
871	>	sw, w.nextSpare))
872	>	w.shutdown(false);
873	>	}
874	>
875	>	/**
876	>	* Does at most one of:
877	>	*
878	>	* 1. Help wake up existing workers waiting for work via
879	>	*    releaseEventWaiters. (If any exist, then it probably doesn't
880	>	*    matter right now if under target parallelism level.)
881	>	*
882	>	* 2. If below parallelism level and a spare exists, try (once)
883	>	*    to resume it via tryResumeSpare.
884	>	*
885	>	* 3. If neither of the above, tries (once) to add a new
886	>	*    worker if either there are not enough total, or if all
887	>	*    existing workers are busy, there are either no running
888	>	*    workers or the deficit is at least twice the surplus.
889	>	*/
890	>	private void helpMaintainParallelism() {
891	>	// uglified to work better when not compiled
892	>	int pc, wc, rc, tc, rs; long h;
893	>	if ((h = eventWaiters) != 0L) {
894	>	if ((int)(h >>> EVENT_COUNT_SHIFT) != eventCount)
895	>	releaseEventWaiters(false); // avoid useless call
896	>	}
897	>	else if ((pc = parallelism) >
898	>	(rc = ((wc = workerCounts) & RUNNING_COUNT_MASK))) {
899	>	if (spareWaiters != 0)
900	>	tryResumeSpare();
901	>	else if ((rs = runState) < TERMINATING &&
902	>	((tc = wc >>> TOTAL_COUNT_SHIFT) < pc ||
903	>	(tc == (rs & ACTIVE_COUNT_MASK) && // all busy
904	>	(rc == 0 ||                       // must add
905	>	rc < pc - ((tc - pc) << 1)) &&   // within slack
906	>	tc < MAX_WORKERS && runState == rs)) && // recheck busy
907	>	workerCounts == wc &&
908	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset, wc,
909	>	wc + (ONE_RUNNING|ONE_TOTAL)))
910	>	addWorker();
911	>	}
912	>	}
913	>
914	>	/**
915	>	* Callback from workers invoked upon each top-level action (i.e.,
916	>	* stealing a task or taking a submission and running
917	>	* it). Performs one or more of the following:
918	>	*
919	>	* 1. If the worker cannot find work (misses > 0), updates its
920	>	*    active status to inactive and updates activeCount unless
921	>	*    this is the first miss and there is contention, in which
922	>	*    case it may try again (either in this or a subsequent
923	>	*    call).
924	>	*
925	>	* 2. If there are at least 2 misses, awaits the next task event
926	>	*    via eventSync
927	>	*
928	>	* 3. If there are too many running threads, suspends this worker
929	>	*    (first forcing inactivation if necessary).  If it is not
930	>	*    needed, it may be killed while suspended via
931	>	*    tryTrimSpare. Otherwise, upon resume it rechecks to make
932	>	*    sure that it is still needed.
933	>	*
934	>	* 4. Helps release and/or reactivate other workers via
935	>	*    helpMaintainParallelism
936	>	*
937	>	* @param w the worker
938	>	* @param misses the number of scans by caller failing to find work
939	>	* (saturating at 2 just to avoid wraparound)
940	>	*/
941	>	final void preStep(ForkJoinWorkerThread w, int misses) {
942	>	boolean active = w.active;
943	>	int pc = parallelism;
944	>	for (;;) {
945	>	int wc = workerCounts;
946	>	int rc = wc & RUNNING_COUNT_MASK;
947	>	if (active && (misses > 0 || rc > pc)) {
948	>	int rs;                      // try inactivate
949	>	if (UNSAFE.compareAndSwapInt(this, runStateOffset,
950	>	rs = runState, rs - ONE_ACTIVE))
951	>	active = w.active = false;
952	>	else if (misses > 1 || rc > pc ||
953	>	(rs & ACTIVE_COUNT_MASK) >= pc)
954	>	continue;                // force inactivate
955	>	}
956	>	if (misses > 1) {
957	>	misses = 0;                  // don't re-sync
958	>	eventSync(w);                // continue loop to recheck rc
959	>	}
960	>	else if (rc > pc) {
961	>	if (workerCounts == wc &&   // try to suspend as spare
962	>	UNSAFE.compareAndSwapInt(this, workerCountsOffset,
963	>	wc, wc - ONE_RUNNING) &&
964	>	!w.suspendAsSpare())    // false if killed
965	>	break;
966	>	}
967	>	else {
968	>	if (rc < pc || eventWaiters != 0L)
969	>	helpMaintainParallelism();
970	>	break;
971	>	}
972		}
973		}
974
975		/**
976	<	* Initialize workers if necessary
977	<	*/
978	<	final void ensureWorkerInitialization() {
979	<	ForkJoinWorkerThread[] ws = workers;
980	<	if (ws == null) {
981	<	final ReentrantLock lock = this.workerLock;
982	<	lock.lock();
983	<	try {
984	<	ws = workers;
985	<	if (ws == null) {
986	<	int ps = parallelism;
987	<	ws = ensureWorkerArrayCapacity(ps);
988	<	for (int i = 0; i < ps; ++i) {
989	<	ForkJoinWorkerThread w = createWorker(i);
990	<	if (w != null) {
991	<	ws[i] = w;
992	<	w.start();
993	<	updateWorkerCount(1);
994	<	}
995	<	}
996	<	}
997	<	} finally {
998	<	lock.unlock();
976	>	* Helps and/or blocks awaiting join of the given task.
977	>	* Alternates between helpJoinTask() and helpMaintainParallelism()
978	>	* as many times as there is a deficit in running count (or longer
979	>	* if running count would become zero), then blocks if task still
980	>	* not done.
981	>	*
982	>	* @param joinMe the task to join
983	>	*/
984	>	final void awaitJoin(ForkJoinTask<?> joinMe, ForkJoinWorkerThread worker) {
985	>	int threshold = parallelism;         // descend blocking thresholds
986	>	while (joinMe.status >= 0) {
987	>	boolean block; int wc;
988	>	worker.helpJoinTask(joinMe);
989	>	if (joinMe.status < 0)
990	>	break;
991	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
992	>	if (threshold > 0)
993	>	--threshold;
994	>	else
995	>	advanceEventCount(); // force release
996	>	block = false;
997	>	}
998	>	else
999	>	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1000	>	wc, wc - ONE_RUNNING);
1001	>	helpMaintainParallelism();
1002	>	if (block) {
1003	>	int c;
1004	>	joinMe.internalAwaitDone();
1005	>	do {} while (!UNSAFE.compareAndSwapInt
1006	>	(this, workerCountsOffset,
1007	>	c = workerCounts, c + ONE_RUNNING));
1008	>	break;
1009		}
1010		}
1011		}
1012
1013		/**
1014	<	* Worker creation and startup for threads added via setParallelism.
1014	>	* Same idea as awaitJoin, but no helping
1015		*/
1016	<	private void createAndStartAddedWorkers() {
1017	<	resumeAllSpares();  // Allow spares to convert to nonspare
1018	<	int ps = parallelism;
1019	<	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(ps);
1020	<	int len = ws.length;
1021	<	// Sweep through slots, to keep lowest indices most populated
1022	<	int k = 0;
1023	<	while (k < len) {
1024	<	if (ws[k] != null) {
1025	<	++k;
1026	<	continue;
1016	>	final void awaitBlocker(ManagedBlocker blocker)
1017	>	throws InterruptedException {
1018	>	int threshold = parallelism;
1019	>	while (!blocker.isReleasable()) {
1020	>	boolean block; int wc;
1021	>	if (((wc = workerCounts) & RUNNING_COUNT_MASK) <= threshold) {
1022	>	if (threshold > 0)
1023	>	--threshold;
1024	>	else
1025	>	advanceEventCount();
1026	>	block = false;
1027		}
1028	<	int s = workerCounts;
1029	<	int tc = totalCountOf(s);
1030	<	int rc = runningCountOf(s);
1031	<	if (rc >= ps || tc >= ps)
1028	>	else
1029	>	block = UNSAFE.compareAndSwapInt(this, workerCountsOffset,
1030	>	wc, wc - ONE_RUNNING);
1031	>	helpMaintainParallelism();
1032	>	if (block) {
1033	>	try {
1034	>	do {} while (!blocker.isReleasable() && !blocker.block());
1035	>	} finally {
1036	>	int c;
1037	>	do {} while (!UNSAFE.compareAndSwapInt
1038	>	(this, workerCountsOffset,
1039	>	c = workerCounts, c + ONE_RUNNING));
1040	>	}
1041		break;
1042	<	if (casWorkerCounts (s, workerCountsFor(tc+1, rc+1))) {
1043	<	ForkJoinWorkerThread w = createWorker(k);
1042	>	}
1043	>	}
1044	>	}
1045	>
1046	>	/**
1047	>	* Possibly initiates and/or completes termination.
1048	>	*
1049	>	* @param now if true, unconditionally terminate, else only
1050	>	* if shutdown and empty queue and no active workers
1051	>	* @return true if now terminating or terminated
1052	>	*/
1053	>	private boolean tryTerminate(boolean now) {
1054	>	if (now)
1055	>	advanceRunLevel(SHUTDOWN); // ensure at least SHUTDOWN
1056	>	else if (runState < SHUTDOWN ||
1057	>	!submissionQueue.isEmpty() ||
1058	>	(runState & ACTIVE_COUNT_MASK) != 0)
1059	>	return false;
1060	>
1061	>	if (advanceRunLevel(TERMINATING))
1062	>	startTerminating();
1063	>
1064	>	// Finish now if all threads terminated; else in some subsequent call
1065	>	if ((workerCounts >>> TOTAL_COUNT_SHIFT) == 0) {
1066	>	advanceRunLevel(TERMINATED);
1067	>	termination.arrive();
1068	>	}
1069	>	return true;
1070	>	}
1071	>
1072	>	/**
1073	>	* Actions on transition to TERMINATING
1074	>	*
1075	>	* Runs up to four passes through workers: (0) shutting down each
1076	>	* quietly (without waking up if parked) to quickly spread
1077	>	* notifications without unnecessary bouncing around event queues
1078	>	* etc (1) wake up and help cancel tasks (2) interrupt (3) mop up
1079	>	* races with interrupted workers
1080	>	*/
1081	>	private void startTerminating() {
1082	>	cancelSubmissions();
1083	>	for (int passes = 0; passes < 4 && workerCounts != 0; ++passes) {
1084	>	advanceEventCount();
1085	>	eventWaiters = 0L; // clobber lists
1086	>	spareWaiters = 0;
1087	>	ForkJoinWorkerThread[] ws = workers;
1088	>	int n = ws.length;
1089	>	for (int i = 0; i < n; ++i) {
1090	>	ForkJoinWorkerThread w = ws[i];
1091		if (w != null) {
1092	<	ws[k++] = w;
1093	<	w.start();
1094	<	}
1095	<	else {
1096	<	updateWorkerCount(-1); // back out on failed creation
1097	<	break;
1092	>	w.shutdown(true);
1093	>	if (passes > 0 && !w.isTerminated()) {
1094	>	w.cancelTasks();
1095	>	LockSupport.unpark(w);
1096	>	if (passes > 1) {
1097	>	try {
1098	>	w.interrupt();
1099	>	} catch (SecurityException ignore) {
1100	>	}
1101	>	}
1102	>	}
1103		}
1104		}
1105		}
1106		}
1107
1108	+	/**
1109	+	* Clear out and cancel submissions, ignoring exceptions
1110	+	*/
1111	+	private void cancelSubmissions() {
1112	+	ForkJoinTask<?> task;
1113	+	while ((task = submissionQueue.poll()) != null) {
1114	+	try {
1115	+	task.cancel(false);
1116	+	} catch (Throwable ignore) {
1117	+	}
1118	+	}
1119	+	}
1120	+
1121	+	// misc support for ForkJoinWorkerThread
1122	+
1123	+	/**
1124	+	* Returns pool number
1125	+	*/
1126	+	final int getPoolNumber() {
1127	+	return poolNumber;
1128	+	}
1129	+
1130	+	/**
1131	+	* Tries to accumulates steal count from a worker, clearing
1132	+	* the worker's value.
1133	+	*
1134	+	* @return true if worker steal count now zero
1135	+	*/
1136	+	final boolean tryAccumulateStealCount(ForkJoinWorkerThread w) {
1137	+	int sc = w.stealCount;
1138	+	long c = stealCount;
1139	+	// CAS even if zero, for fence effects
1140	+	if (UNSAFE.compareAndSwapLong(this, stealCountOffset, c, c + sc)) {
1141	+	if (sc != 0)
1142	+	w.stealCount = 0;
1143	+	return true;
1144	+	}
1145	+	return sc == 0;
1146	+	}
1147	+
1148	+	/**
1149	+	* Returns the approximate (non-atomic) number of idle threads per
1150	+	* active thread.
1151	+	*/
1152	+	final int idlePerActive() {
1153	+	int pc = parallelism; // use parallelism, not rc
1154	+	int ac = runState;    // no mask -- artifically boosts during shutdown
1155	+	// Use exact results for small values, saturate past 4
1156	+	return pc <= ac? 0 : pc >>> 1 <= ac? 1 : pc >>> 2 <= ac? 3 : pc >>> 3;
1157	+	}
1158	+
1159	+	// Public and protected methods
1160	+
1161	+	// Constructors
1162	+
1163	+	/**
1164	+	* Creates a {@code ForkJoinPool} with parallelism equal to {@link
1165	+	* java.lang.Runtime#availableProcessors}, using the {@linkplain
1166	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1167	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1168	+	*
1169	+	* @throws SecurityException if a security manager exists and
1170	+	*         the caller is not permitted to modify threads
1171	+	*         because it does not hold {@link
1172	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1173	+	*/
1174	+	public ForkJoinPool() {
1175	+	this(Runtime.getRuntime().availableProcessors(),
1176	+	defaultForkJoinWorkerThreadFactory, null, false);
1177	+	}
1178	+
1179	+	/**
1180	+	* Creates a {@code ForkJoinPool} with the indicated parallelism
1181	+	* level, the {@linkplain
1182	+	* #defaultForkJoinWorkerThreadFactory default thread factory},
1183	+	* no UncaughtExceptionHandler, and non-async LIFO processing mode.
1184	+	*
1185	+	* @param parallelism the parallelism level
1186	+	* @throws IllegalArgumentException if parallelism less than or
1187	+	*         equal to zero, or greater than implementation limit
1188	+	* @throws SecurityException if a security manager exists and
1189	+	*         the caller is not permitted to modify threads
1190	+	*         because it does not hold {@link
1191	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1192	+	*/
1193	+	public ForkJoinPool(int parallelism) {
1194	+	this(parallelism, defaultForkJoinWorkerThreadFactory, null, false);
1195	+	}
1196	+
1197	+	/**
1198	+	* Creates a {@code ForkJoinPool} with the given parameters.
1199	+	*
1200	+	* @param parallelism the parallelism level. For default value,
1201	+	* use {@link java.lang.Runtime#availableProcessors}.
1202	+	* @param factory the factory for creating new threads. For default value,
1203	+	* use {@link #defaultForkJoinWorkerThreadFactory}.
1204	+	* @param handler the handler for internal worker threads that
1205	+	* terminate due to unrecoverable errors encountered while executing
1206	+	* tasks. For default value, use <code>null</code>.
1207	+	* @param asyncMode if true,
1208	+	* establishes local first-in-first-out scheduling mode for forked
1209	+	* tasks that are never joined. This mode may be more appropriate
1210	+	* than default locally stack-based mode in applications in which
1211	+	* worker threads only process event-style asynchronous tasks.
1212	+	* For default value, use <code>false</code>.
1213	+	* @throws IllegalArgumentException if parallelism less than or
1214	+	*         equal to zero, or greater than implementation limit
1215	+	* @throws NullPointerException if the factory is null
1216	+	* @throws SecurityException if a security manager exists and
1217	+	*         the caller is not permitted to modify threads
1218	+	*         because it does not hold {@link
1219	+	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1220	+	*/
1221	+	public ForkJoinPool(int parallelism,
1222	+	ForkJoinWorkerThreadFactory factory,
1223	+	Thread.UncaughtExceptionHandler handler,
1224	+	boolean asyncMode) {
1225	+	checkPermission();
1226	+	if (factory == null)
1227	+	throw new NullPointerException();
1228	+	if (parallelism <= 0 || parallelism > MAX_WORKERS)
1229	+	throw new IllegalArgumentException();
1230	+	this.parallelism = parallelism;
1231	+	this.factory = factory;
1232	+	this.ueh = handler;
1233	+	this.locallyFifo = asyncMode;
1234	+	int arraySize = initialArraySizeFor(parallelism);
1235	+	this.workers = new ForkJoinWorkerThread[arraySize];
1236	+	this.submissionQueue = new LinkedTransferQueue<ForkJoinTask<?>>();
1237	+	this.workerLock = new ReentrantLock();
1238	+	this.termination = new Phaser(1);
1239	+	this.poolNumber = poolNumberGenerator.incrementAndGet();
1240	+	this.trimTime = System.nanoTime();
1241	+	}
1242	+
1243	+	/**
1244	+	* Returns initial power of two size for workers array.
1245	+	* @param pc the initial parallelism level
1246	+	*/
1247	+	private static int initialArraySizeFor(int pc) {
1248	+	// See Hackers Delight, sec 3.2. We know MAX_WORKERS < (1 >>> 16)
1249	+	int size = pc < MAX_WORKERS ? pc + 1 : MAX_WORKERS;
1250	+	size |= size >>> 1;
1251	+	size |= size >>> 2;
1252	+	size |= size >>> 4;
1253	+	size |= size >>> 8;
1254	+	return size + 1;
1255	+	}
1256	+
1257		// Execution methods
1258
1259		/**
1260		* Common code for execute, invoke and submit
1261		*/
1262		private <T> void doSubmit(ForkJoinTask<T> task) {
1263	<	if (isShutdown())
1263	>	if (task == null)
1264	>	throw new NullPointerException();
1265	>	if (runState >= SHUTDOWN)
1266		throw new RejectedExecutionException();
536	–	if (workers == null)
537	–	ensureWorkerInitialization();
1267		submissionQueue.offer(task);
1268	<	signalIdleWorkers();
1268	>	advanceEventCount();
1269	>	helpMaintainParallelism();         // start or wake up workers
1270		}
1271
1272		/**
1273	<	* Performs the given task; returning its result upon completion
1273	>	* Performs the given task, returning its result upon completion.
1274	>	*
1275		* @param task the task
1276		* @return the task's result
1277	<	* @throws NullPointerException if task is null
1278	<	* @throws RejectedExecutionException if pool is shut down
1277	>	* @throws NullPointerException if the task is null
1278	>	* @throws RejectedExecutionException if the task cannot be
1279	>	*         scheduled for execution
1280		*/
1281		public <T> T invoke(ForkJoinTask<T> task) {
1282		doSubmit(task);
#	Line 553 | Line 1285 | public class ForkJoinPool extends Abstra
1285
1286		/**
1287		* Arranges for (asynchronous) execution of the given task.
1288	+	* If the caller is already engaged in a fork/join computation in
1289	+	* the current pool, this method is equivalent in effect to
1290	+	* {@link ForkJoinTask#fork}.
1291	+	*
1292		* @param task the task
1293	<	* @throws NullPointerException if task is null
1294	<	* @throws RejectedExecutionException if pool is shut down
1293	>	* @throws NullPointerException if the task is null
1294	>	* @throws RejectedExecutionException if the task cannot be
1295	>	*         scheduled for execution
1296		*/
1297	<	public <T> void execute(ForkJoinTask<T> task) {
1297	>	public void execute(ForkJoinTask<?> task) {
1298		doSubmit(task);
1299		}
1300
1301		// AbstractExecutorService methods
1302
1303	+	/**
1304	+	* @throws NullPointerException if the task is null
1305	+	* @throws RejectedExecutionException if the task cannot be
1306	+	*         scheduled for execution
1307	+	*/
1308		public void execute(Runnable task) {
1309	<	doSubmit(new AdaptedRunnable<Void>(task, null));
1309	>	ForkJoinTask<?> job;
1310	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1311	>	job = (ForkJoinTask<?>) task;
1312	>	else
1313	>	job = ForkJoinTask.adapt(task, null);
1314	>	doSubmit(job);
1315		}
1316
1317	+	/**
1318	+	* Submits a ForkJoinTask for execution.
1319	+	* If the caller is already engaged in a fork/join computation in
1320	+	* the current pool, this method is equivalent in effect to
1321	+	* {@link ForkJoinTask#fork}.
1322	+	*
1323	+	* @param task the task to submit
1324	+	* @return the task
1325	+	* @throws NullPointerException if the task is null
1326	+	* @throws RejectedExecutionException if the task cannot be
1327	+	*         scheduled for execution
1328	+	*/
1329	+	public <T> ForkJoinTask<T> submit(ForkJoinTask<T> task) {
1330	+	doSubmit(task);
1331	+	return task;
1332	+	}
1333	+
1334	+	/**
1335	+	* @throws NullPointerException if the task is null
1336	+	* @throws RejectedExecutionException if the task cannot be
1337	+	*         scheduled for execution
1338	+	*/
1339		public <T> ForkJoinTask<T> submit(Callable<T> task) {
1340	<	ForkJoinTask<T> job = new AdaptedCallable<T>(task);
1340	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task);
1341		doSubmit(job);
1342		return job;
1343		}
1344
1345	+	/**
1346	+	* @throws NullPointerException if the task is null
1347	+	* @throws RejectedExecutionException if the task cannot be
1348	+	*         scheduled for execution
1349	+	*/
1350		public <T> ForkJoinTask<T> submit(Runnable task, T result) {
1351	<	ForkJoinTask<T> job = new AdaptedRunnable<T>(task, result);
1351	>	ForkJoinTask<T> job = ForkJoinTask.adapt(task, result);
1352		doSubmit(job);
1353		return job;
1354		}
1355
1356	+	/**
1357	+	* @throws NullPointerException if the task is null
1358	+	* @throws RejectedExecutionException if the task cannot be
1359	+	*         scheduled for execution
1360	+	*/
1361		public ForkJoinTask<?> submit(Runnable task) {
1362	<	ForkJoinTask<Void> job = new AdaptedRunnable<Void>(task, null);
1362	>	ForkJoinTask<?> job;
1363	>	if (task instanceof ForkJoinTask<?>) // avoid re-wrap
1364	>	job = (ForkJoinTask<?>) task;
1365	>	else
1366	>	job = ForkJoinTask.adapt(task, null);
1367		doSubmit(job);
1368		return job;
1369		}
1370
1371		/**
1372	<	* Adaptor for Runnables. This implements RunnableFuture
1373	<	* to be compliant with AbstractExecutorService constraints
1372	>	* @throws NullPointerException       {@inheritDoc}
1373	>	* @throws RejectedExecutionException {@inheritDoc}
1374		*/
592	–	static final class AdaptedRunnable<T> extends ForkJoinTask<T>
593	–	implements RunnableFuture<T> {
594	–	final Runnable runnable;
595	–	final T resultOnCompletion;
596	–	T result;
597	–	AdaptedRunnable(Runnable runnable, T result) {
598	–	if (runnable == null) throw new NullPointerException();
599	–	this.runnable = runnable;
600	–	this.resultOnCompletion = result;
601	–	}
602	–	public T getRawResult() { return result; }
603	–	public void setRawResult(T v) { result = v; }
604	–	public boolean exec() {
605	–	runnable.run();
606	–	result = resultOnCompletion;
607	–	return true;
608	–	}
609	–	public void run() { invoke(); }
610	–	}
611	–
612	–	/**
613	–	* Adaptor for Callables
614	–	*/
615	–	static final class AdaptedCallable<T> extends ForkJoinTask<T>
616	–	implements RunnableFuture<T> {
617	–	final Callable<T> callable;
618	–	T result;
619	–	AdaptedCallable(Callable<T> callable) {
620	–	if (callable == null) throw new NullPointerException();
621	–	this.callable = callable;
622	–	}
623	–	public T getRawResult() { return result; }
624	–	public void setRawResult(T v) { result = v; }
625	–	public boolean exec() {
626	–	try {
627	–	result = callable.call();
628	–	return true;
629	–	} catch (Error err) {
630	–	throw err;
631	–	} catch (RuntimeException rex) {
632	–	throw rex;
633	–	} catch (Exception ex) {
634	–	throw new RuntimeException(ex);
635	–	}
636	–	}
637	–	public void run() { invoke(); }
638	–	}
639	–
1375		public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks) {
1376	<	ArrayList<ForkJoinTask<T>> ts =
1376	>	ArrayList<ForkJoinTask<T>> forkJoinTasks =
1377		new ArrayList<ForkJoinTask<T>>(tasks.size());
1378	<	for (Callable<T> c : tasks)
1379	<	ts.add(new AdaptedCallable<T>(c));
1380	<	invoke(new InvokeAll<T>(ts));
1381	<	return (List<Future<T>>)(List)ts;
1378	>	for (Callable<T> task : tasks)
1379	>	forkJoinTasks.add(ForkJoinTask.adapt(task));
1380	>	invoke(new InvokeAll<T>(forkJoinTasks));
1381	>
1382	>	@SuppressWarnings({"unchecked", "rawtypes"})
1383	>	List<Future<T>> futures = (List<Future<T>>) (List) forkJoinTasks;
1384	>	return futures;
1385		}
1386
1387		static final class InvokeAll<T> extends RecursiveAction {
1388		final ArrayList<ForkJoinTask<T>> tasks;
1389		InvokeAll(ArrayList<ForkJoinTask<T>> tasks) { this.tasks = tasks; }
1390		public void compute() {
1391	<	try { invokeAll(tasks); } catch(Exception ignore) {}
1391	>	try { invokeAll(tasks); }
1392	>	catch (Exception ignore) {}
1393		}
1394	+	private static final long serialVersionUID = -7914297376763021607L;
1395		}
1396
657	–	// Configuration and status settings and queries
658	–
1397		/**
1398	<	* Returns the factory used for constructing new workers
1398	>	* Returns the factory used for constructing new workers.
1399		*
1400		* @return the factory used for constructing new workers
1401		*/
#	Line 668 | Line 1406 | public class ForkJoinPool extends Abstra
1406		/**
1407		* Returns the handler for internal worker threads that terminate
1408		* due to unrecoverable errors encountered while executing tasks.
671	–	* @return the handler, or null if none
672	–	*/
673	–	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
674	–	Thread.UncaughtExceptionHandler h;
675	–	final ReentrantLock lock = this.workerLock;
676	–	lock.lock();
677	–	try {
678	–	h = ueh;
679	–	} finally {
680	–	lock.unlock();
681	–	}
682	–	return h;
683	–	}
684	–
685	–	/**
686	–	* Sets the handler for internal worker threads that terminate due
687	–	* to unrecoverable errors encountered while executing tasks.
688	–	* Unless set, the current default or ThreadGroup handler is used
689	–	* as handler.
1409		*
1410	<	* @param h the new handler
692	<	* @return the old handler, or null if none
693	<	* @throws SecurityException if a security manager exists and
694	<	*         the caller is not permitted to modify threads
695	<	*         because it does not hold {@link
696	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
697	<	*/
698	<	public Thread.UncaughtExceptionHandler
699	<	setUncaughtExceptionHandler(Thread.UncaughtExceptionHandler h) {
700	<	checkPermission();
701	<	Thread.UncaughtExceptionHandler old = null;
702	<	final ReentrantLock lock = this.workerLock;
703	<	lock.lock();
704	<	try {
705	<	old = ueh;
706	<	ueh = h;
707	<	ForkJoinWorkerThread[] ws = workers;
708	<	if (ws != null) {
709	<	for (int i = 0; i < ws.length; ++i) {
710	<	ForkJoinWorkerThread w = ws[i];
711	<	if (w != null)
712	<	w.setUncaughtExceptionHandler(h);
713	<	}
714	<	}
715	<	} finally {
716	<	lock.unlock();
717	<	}
718	<	return old;
719	<	}
720	<
721	<
722	<	/**
723	<	* Sets the target parallelism level of this pool.
724	<	* @param parallelism the target parallelism
725	<	* @throws IllegalArgumentException if parallelism less than or
726	<	* equal to zero or greater than maximum size bounds
727	<	* @throws SecurityException if a security manager exists and
728	<	*         the caller is not permitted to modify threads
729	<	*         because it does not hold {@link
730	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
1410	>	* @return the handler, or {@code null} if none
1411		*/
1412	<	public void setParallelism(int parallelism) {
1413	<	checkPermission();
734	<	if (parallelism <= 0 || parallelism > maxPoolSize)
735	<	throw new IllegalArgumentException();
736	<	final ReentrantLock lock = this.workerLock;
737	<	lock.lock();
738	<	try {
739	<	if (!isTerminating()) {
740	<	int p = this.parallelism;
741	<	this.parallelism = parallelism;
742	<	if (parallelism > p)
743	<	createAndStartAddedWorkers();
744	<	else
745	<	trimSpares();
746	<	}
747	<	} finally {
748	<	lock.unlock();
749	<	}
750	<	signalIdleWorkers();
1412	>	public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
1413	>	return ueh;
1414		}
1415
1416		/**
1417	<	* Returns the targeted number of worker threads in this pool.
1417	>	* Returns the targeted parallelism level of this pool.
1418		*
1419	<	* @return the targeted number of worker threads in this pool
1419	>	* @return the targeted parallelism level of this pool
1420		*/
1421		public int getParallelism() {
1422		return parallelism;
#	Line 762 | Line 1425 | public class ForkJoinPool extends Abstra
1425		/**
1426		* Returns the number of worker threads that have started but not
1427		* yet terminated.  This result returned by this method may differ
1428	<	* from {@code getParallelism} when threads are created to
1428	>	* from {@link #getParallelism} when threads are created to
1429		* maintain parallelism when others are cooperatively blocked.
1430		*
1431		* @return the number of worker threads
1432		*/
1433		public int getPoolSize() {
1434	<	return totalCountOf(workerCounts);
772	<	}
773	<
774	<	/**
775	<	* Returns the maximum number of threads allowed to exist in the
776	<	* pool, even if there are insufficient unblocked running threads.
777	<	* @return the maximum
778	<	*/
779	<	public int getMaximumPoolSize() {
780	<	return maxPoolSize;
781	<	}
782	<
783	<	/**
784	<	* Sets the maximum number of threads allowed to exist in the
785	<	* pool, even if there are insufficient unblocked running threads.
786	<	* Setting this value has no effect on current pool size. It
787	<	* controls construction of new threads.
788	<	* @throws IllegalArgumentException if negative or greater then
789	<	* internal implementation limit
790	<	*/
791	<	public void setMaximumPoolSize(int newMax) {
792	<	if (newMax < 0 || newMax > MAX_THREADS)
793	<	throw new IllegalArgumentException();
794	<	maxPoolSize = newMax;
795	<	}
796	<
797	<
798	<	/**
799	<	* Returns true if this pool dynamically maintains its target
800	<	* parallelism level. If false, new threads are added only to
801	<	* avoid possible starvation.
802	<	* This setting is by default true;
803	<	* @return true if maintains parallelism
804	<	*/
805	<	public boolean getMaintainsParallelism() {
806	<	return maintainsParallelism;
807	<	}
808	<
809	<	/**
810	<	* Sets whether this pool dynamically maintains its target
811	<	* parallelism level. If false, new threads are added only to
812	<	* avoid possible starvation.
813	<	* @param enable true to maintains parallelism
814	<	*/
815	<	public void setMaintainsParallelism(boolean enable) {
816	<	maintainsParallelism = enable;
1434	>	return workerCounts >>> TOTAL_COUNT_SHIFT;
1435		}
1436
1437		/**
1438	<	* Establishes local first-in-first-out scheduling mode for forked
821	<	* tasks that are never joined. This mode may be more appropriate
822	<	* than default locally stack-based mode in applications in which
823	<	* worker threads only process asynchronous tasks.  This method is
824	<	* designed to be invoked only when pool is quiescent, and
825	<	* typically only before any tasks are submitted. The effects of
826	<	* invocations at other times may be unpredictable.
827	<	*
828	<	* @param async if true, use locally FIFO scheduling
829	<	* @return the previous mode
830	<	*/
831	<	public boolean setAsyncMode(boolean async) {
832	<	boolean oldMode = locallyFifo;
833	<	locallyFifo = async;
834	<	ForkJoinWorkerThread[] ws = workers;
835	<	if (ws != null) {
836	<	for (int i = 0; i < ws.length; ++i) {
837	<	ForkJoinWorkerThread t = ws[i];
838	<	if (t != null)
839	<	t.setAsyncMode(async);
840	<	}
841	<	}
842	<	return oldMode;
843	<	}
844	<
845	<	/**
846	<	* Returns true if this pool uses local first-in-first-out
1438	>	* Returns {@code true} if this pool uses local first-in-first-out
1439		* scheduling mode for forked tasks that are never joined.
1440		*
1441	<	* @return true if this pool uses async mode
1441	>	* @return {@code true} if this pool uses async mode
1442		*/
1443		public boolean getAsyncMode() {
1444		return locallyFifo;
#	Line 855 | Line 1447 | public class ForkJoinPool extends Abstra
1447		/**
1448		* Returns an estimate of the number of worker threads that are
1449		* not blocked waiting to join tasks or for other managed
1450	<	* synchronization.
1450	>	* synchronization. This method may overestimate the
1451	>	* number of running threads.
1452		*
1453		* @return the number of worker threads
1454		*/
1455		public int getRunningThreadCount() {
1456	<	return runningCountOf(workerCounts);
1456	>	return workerCounts & RUNNING_COUNT_MASK;
1457		}
1458
1459		/**
1460		* Returns an estimate of the number of threads that are currently
1461		* stealing or executing tasks. This method may overestimate the
1462		* number of active threads.
1463	+	*
1464		* @return the number of active threads
1465		*/
1466		public int getActiveThreadCount() {
1467	<	return activeCountOf(runControl);
874	<	}
875	<
876	<	/**
877	<	* Returns an estimate of the number of threads that are currently
878	<	* idle waiting for tasks. This method may underestimate the
879	<	* number of idle threads.
880	<	* @return the number of idle threads
881	<	*/
882	<	final int getIdleThreadCount() {
883	<	int c = runningCountOf(workerCounts) - activeCountOf(runControl);
884	<	return (c <= 0)? 0 : c;
1467	>	return runState & ACTIVE_COUNT_MASK;
1468		}
1469
1470		/**
1471	<	* Returns true if all worker threads are currently idle. An idle
1472	<	* worker is one that cannot obtain a task to execute because none
1473	<	* are available to steal from other threads, and there are no
1474	<	* pending submissions to the pool. This method is conservative:
1475	<	* It might not return true immediately upon idleness of all
1476	<	* threads, but will eventually become true if threads remain
1477	<	* inactive.
1478	<	* @return true if all threads are currently idle
1471	>	* Returns {@code true} if all worker threads are currently idle.
1472	>	* An idle worker is one that cannot obtain a task to execute
1473	>	* because none are available to steal from other threads, and
1474	>	* there are no pending submissions to the pool. This method is
1475	>	* conservative; it might not return {@code true} immediately upon
1476	>	* idleness of all threads, but will eventually become true if
1477	>	* threads remain inactive.
1478	>	*
1479	>	* @return {@code true} if all threads are currently idle
1480		*/
1481		public boolean isQuiescent() {
1482	<	return activeCountOf(runControl) == 0;
1482	>	return (runState & ACTIVE_COUNT_MASK) == 0;
1483		}
1484
1485		/**
#	Line 903 | Line 1487 | public class ForkJoinPool extends Abstra
1487		* one thread's work queue by another. The reported value
1488		* underestimates the actual total number of steals when the pool
1489		* is not quiescent. This value may be useful for monitoring and
1490	<	* tuning fork/join programs: In general, steal counts should be
1490	>	* tuning fork/join programs: in general, steal counts should be
1491		* high enough to keep threads busy, but low enough to avoid
1492		* overhead and contention across threads.
1493	+	*
1494		* @return the number of steals
1495		*/
1496		public long getStealCount() {
1497	<	return stealCount.get();
913	<	}
914	<
915	<	/**
916	<	* Accumulate steal count from a worker. Call only
917	<	* when worker known to be idle.
918	<	*/
919	<	private void updateStealCount(ForkJoinWorkerThread w) {
920	<	int sc = w.getAndClearStealCount();
921	<	if (sc != 0)
922	<	stealCount.addAndGet(sc);
1497	>	return stealCount;
1498		}
1499
1500		/**
#	Line 929 | Line 1504 | public class ForkJoinPool extends Abstra
1504		* an approximation, obtained by iterating across all threads in
1505		* the pool. This method may be useful for tuning task
1506		* granularities.
1507	+	*
1508		* @return the number of queued tasks
1509		*/
1510		public long getQueuedTaskCount() {
1511		long count = 0;
1512		ForkJoinWorkerThread[] ws = workers;
1513	<	if (ws != null) {
1514	<	for (int i = 0; i < ws.length; ++i) {
1515	<	ForkJoinWorkerThread t = ws[i];
1516	<	if (t != null)
1517	<	count += t.getQueueSize();
942	<	}
1513	>	int n = ws.length;
1514	>	for (int i = 0; i < n; ++i) {
1515	>	ForkJoinWorkerThread w = ws[i];
1516	>	if (w != null)
1517	>	count += w.getQueueSize();
1518		}
1519		return count;
1520		}
1521
1522		/**
1523	<	* Returns an estimate of the number tasks submitted to this pool
1524	<	* that have not yet begun executing. This method takes time
1523	>	* Returns an estimate of the number of tasks submitted to this
1524	>	* pool that have not yet begun executing.  This method takes time
1525		* proportional to the number of submissions.
1526	+	*
1527		* @return the number of queued submissions
1528		*/
1529		public int getQueuedSubmissionCount() {
#	Line 955 | Line 1531 | public class ForkJoinPool extends Abstra
1531		}
1532
1533		/**
1534	<	* Returns true if there are any tasks submitted to this pool
1535	<	* that have not yet begun executing.
1534	>	* Returns {@code true} if there are any tasks submitted to this
1535	>	* pool that have not yet begun executing.
1536	>	*
1537		* @return {@code true} if there are any queued submissions
1538		*/
1539		public boolean hasQueuedSubmissions() {
#	Line 967 | Line 1544 | public class ForkJoinPool extends Abstra
1544		* Removes and returns the next unexecuted submission if one is
1545		* available.  This method may be useful in extensions to this
1546		* class that re-assign work in systems with multiple pools.
1547	<	* @return the next submission, or null if none
1547	>	*
1548	>	* @return the next submission, or {@code null} if none
1549		*/
1550		protected ForkJoinTask<?> pollSubmission() {
1551		return submissionQueue.poll();
#	Line 977 | Line 1555 | public class ForkJoinPool extends Abstra
1555		* Removes all available unexecuted submitted and forked tasks
1556		* from scheduling queues and adds them to the given collection,
1557		* without altering their execution status. These may include
1558	<	* artificially generated or wrapped tasks. This method is designed
1559	<	* to be invoked only when the pool is known to be
1558	>	* artificially generated or wrapped tasks. This method is
1559	>	* designed to be invoked only when the pool is known to be
1560		* quiescent. Invocations at other times may not remove all
1561		* tasks. A failure encountered while attempting to add elements
1562		* to collection {@code c} may result in elements being in
#	Line 986 | Line 1564 | public class ForkJoinPool extends Abstra
1564		* exception is thrown.  The behavior of this operation is
1565		* undefined if the specified collection is modified while the
1566		* operation is in progress.
1567	+	*
1568		* @param c the collection to transfer elements into
1569		* @return the number of elements transferred
1570		*/
1571	<	protected int drainTasksTo(Collection<ForkJoinTask<?>> c) {
1572	<	int n = submissionQueue.drainTo(c);
1571	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1572	>	int count = submissionQueue.drainTo(c);
1573		ForkJoinWorkerThread[] ws = workers;
1574	<	if (ws != null) {
1575	<	for (int i = 0; i < ws.length; ++i) {
1576	<	ForkJoinWorkerThread w = ws[i];
1577	<	if (w != null)
1578	<	n += w.drainTasksTo(c);
1000	<	}
1574	>	int n = ws.length;
1575	>	for (int i = 0; i < n; ++i) {
1576	>	ForkJoinWorkerThread w = ws[i];
1577	>	if (w != null)
1578	>	count += w.drainTasksTo(c);
1579		}
1580	<	return n;
1580	>	return count;
1581		}
1582
1583		/**
#	Line 1010 | Line 1588 | public class ForkJoinPool extends Abstra
1588		* @return a string identifying this pool, as well as its state
1589		*/
1590		public String toString() {
1013	–	int ps = parallelism;
1014	–	int wc = workerCounts;
1015	–	int rc = runControl;
1591		long st = getStealCount();
1592		long qt = getQueuedTaskCount();
1593		long qs = getQueuedSubmissionCount();
1594	+	int wc = workerCounts;
1595	+	int tc = wc >>> TOTAL_COUNT_SHIFT;
1596	+	int rc = wc & RUNNING_COUNT_MASK;
1597	+	int pc = parallelism;
1598	+	int rs = runState;
1599	+	int ac = rs & ACTIVE_COUNT_MASK;
1600		return super.toString() +
1601	<	"[" + runStateToString(runStateOf(rc)) +
1602	<	", parallelism = " + ps +
1603	<	", size = " + totalCountOf(wc) +
1604	<	", active = " + activeCountOf(rc) +
1605	<	", running = " + runningCountOf(wc) +
1601	>	"[" + runLevelToString(rs) +
1602	>	", parallelism = " + pc +
1603	>	", size = " + tc +
1604	>	", active = " + ac +
1605	>	", running = " + rc +
1606		", steals = " + st +
1607		", tasks = " + qt +
1608		", submissions = " + qs +
1609		"]";
1610		}
1611
1612	<	private static String runStateToString(int rs) {
1613	<	switch(rs) {
1614	<	case RUNNING: return "Running";
1615	<	case SHUTDOWN: return "Shutting down";
1616	<	case TERMINATING: return "Terminating";
1036	<	case TERMINATED: return "Terminated";
1037	<	default: throw new Error("Unknown run state");
1038	<	}
1612	>	private static String runLevelToString(int s) {
1613	>	return ((s & TERMINATED) != 0 ? "Terminated" :
1614	>	((s & TERMINATING) != 0 ? "Terminating" :
1615	>	((s & SHUTDOWN) != 0 ? "Shutting down" :
1616	>	"Running")));
1617		}
1618
1041	–	// lifecycle control
1042	–
1619		/**
1620		* Initiates an orderly shutdown in which previously submitted
1621		* tasks are executed, but no new tasks will be accepted.
1622		* Invocation has no additional effect if already shut down.
1623		* Tasks that are in the process of being submitted concurrently
1624		* during the course of this method may or may not be rejected.
1625	+	*
1626		* @throws SecurityException if a security manager exists and
1627		*         the caller is not permitted to modify threads
1628		*         because it does not hold {@link
1629	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
1629	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1630		*/
1631		public void shutdown() {
1632		checkPermission();
1633	<	transitionRunStateTo(SHUTDOWN);
1634	<	if (canTerminateOnShutdown(runControl))
1058	<	terminateOnShutdown();
1633	>	advanceRunLevel(SHUTDOWN);
1634	>	tryTerminate(false);
1635		}
1636
1637		/**
1638	<	* Attempts to stop all actively executing tasks, and cancels all
1639	<	* waiting tasks.  Tasks that are in the process of being
1640	<	* submitted or executed concurrently during the course of this
1641	<	* method may or may not be rejected. Unlike some other executors,
1642	<	* this method cancels rather than collects non-executed tasks
1643	<	* upon termination, so always returns an empty list. However, you
1644	<	* can use method {@code drainTasksTo} before invoking this
1645	<	* method to transfer unexecuted tasks to another collection.
1638	>	* Attempts to cancel and/or stop all tasks, and reject all
1639	>	* subsequently submitted tasks.  Tasks that are in the process of
1640	>	* being submitted or executed concurrently during the course of
1641	>	* this method may or may not be rejected. This method cancels
1642	>	* both existing and unexecuted tasks, in order to permit
1643	>	* termination in the presence of task dependencies. So the method
1644	>	* always returns an empty list (unlike the case for some other
1645	>	* Executors).
1646	>	*
1647		* @return an empty list
1648		* @throws SecurityException if a security manager exists and
1649		*         the caller is not permitted to modify threads
1650		*         because it does not hold {@link
1651	<	*         java.lang.RuntimePermission}{@code ("modifyThread")},
1651	>	*         java.lang.RuntimePermission}{@code ("modifyThread")}
1652		*/
1653		public List<Runnable> shutdownNow() {
1654		checkPermission();
1655	<	terminate();
1655	>	tryTerminate(true);
1656		return Collections.emptyList();
1657		}
1658
#	Line 1085 | Line 1662 | public class ForkJoinPool extends Abstra
1662		* @return {@code true} if all tasks have completed following shut down
1663		*/
1664		public boolean isTerminated() {
1665	<	return runStateOf(runControl) == TERMINATED;
1665	>	return runState >= TERMINATED;
1666		}
1667
1668		/**
1669		* Returns {@code true} if the process of termination has
1670	<	* commenced but possibly not yet completed.
1670	>	* commenced but not yet completed.  This method may be useful for
1671	>	* debugging. A return of {@code true} reported a sufficient
1672	>	* period after shutdown may indicate that submitted tasks have
1673	>	* ignored or suppressed interruption, causing this executor not
1674	>	* to properly terminate.
1675		*
1676	<	* @return {@code true} if terminating
1676	>	* @return {@code true} if terminating but not yet terminated
1677		*/
1678		public boolean isTerminating() {
1679	<	return runStateOf(runControl) >= TERMINATING;
1679	>	return (runState & (TERMINATING|TERMINATED)) == TERMINATING;
1680		}
1681
1682		/**
#	Line 1104 | Line 1685 | public class ForkJoinPool extends Abstra
1685		* @return {@code true} if this pool has been shut down
1686		*/
1687		public boolean isShutdown() {
1688	<	return runStateOf(runControl) >= SHUTDOWN;
1688	>	return runState >= SHUTDOWN;
1689		}
1690
1691		/**
#	Line 1120 | Line 1701 | public class ForkJoinPool extends Abstra
1701		*/
1702		public boolean awaitTermination(long timeout, TimeUnit unit)
1703		throws InterruptedException {
1123	–	long nanos = unit.toNanos(timeout);
1124	–	final ReentrantLock lock = this.workerLock;
1125	–	lock.lock();
1704		try {
1705	<	for (;;) {
1706	<	if (isTerminated())
1129	<	return true;
1130	<	if (nanos <= 0)
1131	<	return false;
1132	<	nanos = termination.awaitNanos(nanos);
1133	<	}
1134	<	} finally {
1135	<	lock.unlock();
1136	<	}
1137	<	}
1138	<
1139	<	// Shutdown and termination support
1140	<
1141	<	/**
1142	<	* Callback from terminating worker. Null out the corresponding
1143	<	* workers slot, and if terminating, try to terminate, else try to
1144	<	* shrink workers array.
1145	<	* @param w the worker
1146	<	*/
1147	<	final void workerTerminated(ForkJoinWorkerThread w) {
1148	<	updateStealCount(w);
1149	<	updateWorkerCount(-1);
1150	<	final ReentrantLock lock = this.workerLock;
1151	<	lock.lock();
1152	<	try {
1153	<	ForkJoinWorkerThread[] ws = workers;
1154	<	if (ws != null) {
1155	<	int idx = w.poolIndex;
1156	<	if (idx >= 0 && idx < ws.length && ws[idx] == w)
1157	<	ws[idx] = null;
1158	<	if (totalCountOf(workerCounts) == 0) {
1159	<	terminate(); // no-op if already terminating
1160	<	transitionRunStateTo(TERMINATED);
1161	<	termination.signalAll();
1162	<	}
1163	<	else if (!isTerminating()) {
1164	<	tryShrinkWorkerArray();
1165	<	tryResumeSpare(true); // allow replacement
1166	<	}
1167	<	}
1168	<	} finally {
1169	<	lock.unlock();
1170	<	}
1171	<	signalIdleWorkers();
1172	<	}
1173	<
1174	<	/**
1175	<	* Initiate termination.
1176	<	*/
1177	<	private void terminate() {
1178	<	if (transitionRunStateTo(TERMINATING)) {
1179	<	stopAllWorkers();
1180	<	resumeAllSpares();
1181	<	signalIdleWorkers();
1182	<	cancelQueuedSubmissions();
1183	<	cancelQueuedWorkerTasks();
1184	<	interruptUnterminatedWorkers();
1185	<	signalIdleWorkers(); // resignal after interrupt
1186	<	}
1187	<	}
1188	<
1189	<	/**
1190	<	* Possibly terminates when on shutdown state.
1191	<	*/
1192	<	private void terminateOnShutdown() {
1193	<	if (!hasQueuedSubmissions() && canTerminateOnShutdown(runControl))
1194	<	terminate();
1195	<	}
1196	<
1197	<	/**
1198	<	* Clears out and cancels submissions.
1199	<	*/
1200	<	private void cancelQueuedSubmissions() {
1201	<	ForkJoinTask<?> task;
1202	<	while ((task = pollSubmission()) != null)
1203	<	task.cancel(false);
1204	<	}
1205	<
1206	<	/**
1207	<	* Cleans out worker queues.
1208	<	*/
1209	<	private void cancelQueuedWorkerTasks() {
1210	<	final ReentrantLock lock = this.workerLock;
1211	<	lock.lock();
1212	<	try {
1213	<	ForkJoinWorkerThread[] ws = workers;
1214	<	if (ws != null) {
1215	<	for (int i = 0; i < ws.length; ++i) {
1216	<	ForkJoinWorkerThread t = ws[i];
1217	<	if (t != null)
1218	<	t.cancelTasks();
1219	<	}
1220	<	}
1221	<	} finally {
1222	<	lock.unlock();
1223	<	}
1224	<	}
1225	<
1226	<	/**
1227	<	* Sets each worker's status to terminating. Requires lock to avoid
1228	<	* conflicts with add/remove.
1229	<	*/
1230	<	private void stopAllWorkers() {
1231	<	final ReentrantLock lock = this.workerLock;
1232	<	lock.lock();
1233	<	try {
1234	<	ForkJoinWorkerThread[] ws = workers;
1235	<	if (ws != null) {
1236	<	for (int i = 0; i < ws.length; ++i) {
1237	<	ForkJoinWorkerThread t = ws[i];
1238	<	if (t != null)
1239	<	t.shutdownNow();
1240	<	}
1241	<	}
1242	<	} finally {
1243	<	lock.unlock();
1244	<	}
1245	<	}
1246	<
1247	<	/**
1248	<	* Interrupts all unterminated workers.  This is not required for
1249	<	* sake of internal control, but may help unstick user code during
1250	<	* shutdown.
1251	<	*/
1252	<	private void interruptUnterminatedWorkers() {
1253	<	final ReentrantLock lock = this.workerLock;
1254	<	lock.lock();
1255	<	try {
1256	<	ForkJoinWorkerThread[] ws = workers;
1257	<	if (ws != null) {
1258	<	for (int i = 0; i < ws.length; ++i) {
1259	<	ForkJoinWorkerThread t = ws[i];
1260	<	if (t != null && !t.isTerminated()) {
1261	<	try {
1262	<	t.interrupt();
1263	<	} catch (SecurityException ignore) {
1264	<	}
1265	<	}
1266	<	}
1267	<	}
1268	<	} finally {
1269	<	lock.unlock();
1270	<	}
1271	<	}
1272	<
1273	<
1274	<	/*
1275	<	* Nodes for event barrier to manage idle threads.  Queue nodes
1276	<	* are basic Treiber stack nodes, also used for spare stack.
1277	<	*
1278	<	* The event barrier has an event count and a wait queue (actually
1279	<	* a Treiber stack).  Workers are enabled to look for work when
1280	<	* the eventCount is incremented. If they fail to find work, they
1281	<	* may wait for next count. Upon release, threads help others wake
1282	<	* up.
1283	<	*
1284	<	* Synchronization events occur only in enough contexts to
1285	<	* maintain overall liveness:
1286	<	*
1287	<	*   - Submission of a new task to the pool
1288	<	*   - Resizes or other changes to the workers array
1289	<	*   - pool termination
1290	<	*   - A worker pushing a task on an empty queue
1291	<	*
1292	<	* The case of pushing a task occurs often enough, and is heavy
1293	<	* enough compared to simple stack pushes, to require special
1294	<	* handling: Method signalWork returns without advancing count if
1295	<	* the queue appears to be empty.  This would ordinarily result in
1296	<	* races causing some queued waiters not to be woken up. To avoid
1297	<	* this, the first worker enqueued in method sync (see
1298	<	* syncIsReleasable) rescans for tasks after being enqueued, and
1299	<	* helps signal if any are found. This works well because the
1300	<	* worker has nothing better to do, and so might as well help
1301	<	* alleviate the overhead and contention on the threads actually
1302	<	* doing work.  Also, since event counts increments on task
1303	<	* availability exist to maintain liveness (rather than to force
1304	<	* refreshes etc), it is OK for callers to exit early if
1305	<	* contending with another signaller.
1306	<	*/
1307	<	static final class WaitQueueNode {
1308	<	WaitQueueNode next; // only written before enqueued
1309	<	volatile ForkJoinWorkerThread thread; // nulled to cancel wait
1310	<	final long count; // unused for spare stack
1311	<
1312	<	WaitQueueNode(long c, ForkJoinWorkerThread w) {
1313	<	count = c;
1314	<	thread = w;
1315	<	}
1316	<
1317	<	/**
1318	<	* Wakes up waiter, returning false if known to already
1319	<	*/
1320	<	boolean signal() {
1321	<	ForkJoinWorkerThread t = thread;
1322	<	if (t == null)
1323	<	return false;
1324	<	thread = null;
1325	<	LockSupport.unpark(t);
1326	<	return true;
1327	<	}
1328	<
1329	<	/**
1330	<	* Awaits release on sync.
1331	<	*/
1332	<	void awaitSyncRelease(ForkJoinPool p) {
1333	<	while (thread != null && !p.syncIsReleasable(this))
1334	<	LockSupport.park(this);
1335	<	}
1336	<
1337	<	/**
1338	<	* Awaits resumption as spare.
1339	<	*/
1340	<	void awaitSpareRelease() {
1341	<	while (thread != null) {
1342	<	if (!Thread.interrupted())
1343	<	LockSupport.park(this);
1344	<	}
1345	<	}
1346	<	}
1347	<
1348	<	/**
1349	<	* Ensures that no thread is waiting for count to advance from the
1350	<	* current value of eventCount read on entry to this method, by
1351	<	* releasing waiting threads if necessary.
1352	<	* @return the count
1353	<	*/
1354	<	final long ensureSync() {
1355	<	long c = eventCount;
1356	<	WaitQueueNode q;
1357	<	while ((q = syncStack) != null && q.count < c) {
1358	<	if (casBarrierStack(q, null)) {
1359	<	do {
1360	<	q.signal();
1361	<	} while ((q = q.next) != null);
1362	<	break;
1363	<	}
1364	<	}
1365	<	return c;
1366	<	}
1367	<
1368	<	/**
1369	<	* Increments event count and releases waiting threads.
1370	<	*/
1371	<	private void signalIdleWorkers() {
1372	<	long c;
1373	<	do;while (!casEventCount(c = eventCount, c+1));
1374	<	ensureSync();
1375	<	}
1376	<
1377	<	/**
1378	<	* Signals threads waiting to poll a task. Because method sync
1379	<	* rechecks availability, it is OK to only proceed if queue
1380	<	* appears to be non-empty, and OK to skip under contention to
1381	<	* increment count (since some other thread succeeded).
1382	<	*/
1383	<	final void signalWork() {
1384	<	long c;
1385	<	WaitQueueNode q;
1386	<	if (syncStack != null &&
1387	<	casEventCount(c = eventCount, c+1) &&
1388	<	(((q = syncStack) != null && q.count <= c) &&
1389	<	(!casBarrierStack(q, q.next) || !q.signal())))
1390	<	ensureSync();
1391	<	}
1392	<
1393	<	/**
1394	<	* Waits until event count advances from last value held by
1395	<	* caller, or if excess threads, caller is resumed as spare, or
1396	<	* caller or pool is terminating. Updates caller's event on exit.
1397	<	* @param w the calling worker thread
1398	<	*/
1399	<	final void sync(ForkJoinWorkerThread w) {
1400	<	updateStealCount(w); // Transfer w's count while it is idle
1401	<
1402	<	while (!w.isShutdown() && !isTerminating() && !suspendIfSpare(w)) {
1403	<	long prev = w.lastEventCount;
1404	<	WaitQueueNode node = null;
1405	<	WaitQueueNode h;
1406	<	while (eventCount == prev &&
1407	<	((h = syncStack) == null || h.count == prev)) {
1408	<	if (node == null)
1409	<	node = new WaitQueueNode(prev, w);
1410	<	if (casBarrierStack(node.next = h, node)) {
1411	<	node.awaitSyncRelease(this);
1412	<	break;
1413	<	}
1414	<	}
1415	<	long ec = ensureSync();
1416	<	if (ec != prev) {
1417	<	w.lastEventCount = ec;
1418	<	break;
1419	<	}
1420	<	}
1421	<	}
1422	<
1423	<	/**
1424	<	* Returns true if worker waiting on sync can proceed:
1425	<	*  - on signal (thread == null)
1426	<	*  - on event count advance (winning race to notify vs signaller)
1427	<	*  - on Interrupt
1428	<	*  - if the first queued node, we find work available
1429	<	* If node was not signalled and event count not advanced on exit,
1430	<	* then we also help advance event count.
1431	<	* @return true if node can be released
1432	<	*/
1433	<	final boolean syncIsReleasable(WaitQueueNode node) {
1434	<	long prev = node.count;
1435	<	if (!Thread.interrupted() && node.thread != null &&
1436	<	(node.next != null ||
1437	<	!ForkJoinWorkerThread.hasQueuedTasks(workers)) &&
1438	<	eventCount == prev)
1439	<	return false;
1440	<	if (node.thread != null) {
1441	<	node.thread = null;
1442	<	long ec = eventCount;
1443	<	if (prev <= ec) // help signal
1444	<	casEventCount(ec, ec+1);
1445	<	}
1446	<	return true;
1447	<	}
1448	<
1449	<	/**
1450	<	* Returns true if a new sync event occurred since last call to
1451	<	* sync or this method, if so, updating caller's count.
1452	<	*/
1453	<	final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1454	<	long lc = w.lastEventCount;
1455	<	long ec = ensureSync();
1456	<	if (ec == lc)
1705	>	return termination.awaitAdvanceInterruptibly(0, timeout, unit) > 0;
1706	>	} catch(TimeoutException ex) {
1707		return false;
1458	–	w.lastEventCount = ec;
1459	–	return true;
1460	–	}
1461	–
1462	–	//  Parallelism maintenance
1463	–
1464	–	/**
1465	–	* Decrements running count; if too low, adds spare.
1466	–	*
1467	–	* Conceptually, all we need to do here is add or resume a
1468	–	* spare thread when one is about to block (and remove or
1469	–	* suspend it later when unblocked -- see suspendIfSpare).
1470	–	* However, implementing this idea requires coping with
1471	–	* several problems: We have imperfect information about the
1472	–	* states of threads. Some count updates can and usually do
1473	–	* lag run state changes, despite arrangements to keep them
1474	–	* accurate (for example, when possible, updating counts
1475	–	* before signalling or resuming), especially when running on
1476	–	* dynamic JVMs that don't optimize the infrequent paths that
1477	–	* update counts. Generating too many threads can make these
1478	–	* problems become worse, because excess threads are more
1479	–	* likely to be context-switched with others, slowing them all
1480	–	* down, especially if there is no work available, so all are
1481	–	* busy scanning or idling.  Also, excess spare threads can
1482	–	* only be suspended or removed when they are idle, not
1483	–	* immediately when they aren't needed. So adding threads will
1484	–	* raise parallelism level for longer than necessary.  Also,
1485	–	* FJ applications often encounter highly transient peaks when
1486	–	* many threads are blocked joining, but for less time than it
1487	–	* takes to create or resume spares.
1488	–	*
1489	–	* @param joinMe if non-null, return early if done
1490	–	* @param maintainParallelism if true, try to stay within
1491	–	* target counts, else create only to avoid starvation
1492	–	* @return true if joinMe known to be done
1493	–	*/
1494	–	final boolean preJoin(ForkJoinTask<?> joinMe, boolean maintainParallelism) {
1495	–	maintainParallelism &= maintainsParallelism; // overrride
1496	–	boolean dec = false;  // true when running count decremented
1497	–	while (spareStack == null || !tryResumeSpare(dec)) {
1498	–	int counts = workerCounts;
1499	–	if (dec || (dec = casWorkerCounts(counts, --counts))) { // CAS cheat
1500	–	if (!needSpare(counts, maintainParallelism))
1501	–	break;
1502	–	if (joinMe.status < 0)
1503	–	return true;
1504	–	if (tryAddSpare(counts))
1505	–	break;
1506	–	}
1507	–	}
1508	–	return false;
1509	–	}
1510	–
1511	–	/**
1512	–	* Same idea as preJoin
1513	–	*/
1514	–	final boolean preBlock(ManagedBlocker blocker, boolean maintainParallelism){
1515	–	maintainParallelism &= maintainsParallelism;
1516	–	boolean dec = false;
1517	–	while (spareStack == null || !tryResumeSpare(dec)) {
1518	–	int counts = workerCounts;
1519	–	if (dec || (dec = casWorkerCounts(counts, --counts))) {
1520	–	if (!needSpare(counts, maintainParallelism))
1521	–	break;
1522	–	if (blocker.isReleasable())
1523	–	return true;
1524	–	if (tryAddSpare(counts))
1525	–	break;
1526	–	}
1527	–	}
1528	–	return false;
1529	–	}
1530	–
1531	–	/**
1532	–	* Returns true if a spare thread appears to be needed.  If
1533	–	* maintaining parallelism, returns true when the deficit in
1534	–	* running threads is more than the surplus of total threads, and
1535	–	* there is apparently some work to do.  This self-limiting rule
1536	–	* means that the more threads that have already been added, the
1537	–	* less parallelism we will tolerate before adding another.
1538	–	* @param counts current worker counts
1539	–	* @param maintainParallelism try to maintain parallelism
1540	–	*/
1541	–	private boolean needSpare(int counts, boolean maintainParallelism) {
1542	–	int ps = parallelism;
1543	–	int rc = runningCountOf(counts);
1544	–	int tc = totalCountOf(counts);
1545	–	int runningDeficit = ps - rc;
1546	–	int totalSurplus = tc - ps;
1547	–	return (tc < maxPoolSize &&
1548	–	(rc == 0 || totalSurplus < 0 ||
1549	–	(maintainParallelism &&
1550	–	runningDeficit > totalSurplus &&
1551	–	ForkJoinWorkerThread.hasQueuedTasks(workers))));
1552	–	}
1553	–
1554	–	/**
1555	–	* Adds a spare worker if lock available and no more than the
1556	–	* expected numbers of threads exist.
1557	–	* @return true if successful
1558	–	*/
1559	–	private boolean tryAddSpare(int expectedCounts) {
1560	–	final ReentrantLock lock = this.workerLock;
1561	–	int expectedRunning = runningCountOf(expectedCounts);
1562	–	int expectedTotal = totalCountOf(expectedCounts);
1563	–	boolean success = false;
1564	–	boolean locked = false;
1565	–	// confirm counts while locking; CAS after obtaining lock
1566	–	try {
1567	–	for (;;) {
1568	–	int s = workerCounts;
1569	–	int tc = totalCountOf(s);
1570	–	int rc = runningCountOf(s);
1571	–	if (rc > expectedRunning || tc > expectedTotal)
1572	–	break;
1573	–	if (!locked && !(locked = lock.tryLock()))
1574	–	break;
1575	–	if (casWorkerCounts(s, workerCountsFor(tc+1, rc+1))) {
1576	–	createAndStartSpare(tc);
1577	–	success = true;
1578	–	break;
1579	–	}
1580	–	}
1581	–	} finally {
1582	–	if (locked)
1583	–	lock.unlock();
1584	–	}
1585	–	return success;
1586	–	}
1587	–
1588	–	/**
1589	–	* Adds the kth spare worker. On entry, pool counts are already
1590	–	* adjusted to reflect addition.
1591	–	*/
1592	–	private void createAndStartSpare(int k) {
1593	–	ForkJoinWorkerThread w = null;
1594	–	ForkJoinWorkerThread[] ws = ensureWorkerArrayCapacity(k + 1);
1595	–	int len = ws.length;
1596	–	// Probably, we can place at slot k. If not, find empty slot
1597	–	if (k < len && ws[k] != null) {
1598	–	for (k = 0; k < len && ws[k] != null; ++k)
1599	–	;
1600	–	}
1601	–	if (k < len && !isTerminating() && (w = createWorker(k)) != null) {
1602	–	ws[k] = w;
1603	–	w.start();
1604	–	}
1605	–	else
1606	–	updateWorkerCount(-1); // adjust on failure
1607	–	signalIdleWorkers();
1608	–	}
1609	–
1610	–	/**
1611	–	* Suspends calling thread w if there are excess threads.  Called
1612	–	* only from sync.  Spares are enqueued in a Treiber stack using
1613	–	* the same WaitQueueNodes as barriers.  They are resumed mainly
1614	–	* in preJoin, but are also woken on pool events that require all
1615	–	* threads to check run state.
1616	–	* @param w the caller
1617	–	*/
1618	–	private boolean suspendIfSpare(ForkJoinWorkerThread w) {
1619	–	WaitQueueNode node = null;
1620	–	int s;
1621	–	while (parallelism < runningCountOf(s = workerCounts)) {
1622	–	if (node == null)
1623	–	node = new WaitQueueNode(0, w);
1624	–	if (casWorkerCounts(s, s-1)) { // representation-dependent
1625	–	// push onto stack
1626	–	do;while (!casSpareStack(node.next = spareStack, node));
1627	–	// block until released by resumeSpare
1628	–	node.awaitSpareRelease();
1629	–	return true;
1630	–	}
1631	–	}
1632	–	return false;
1633	–	}
1634	–
1635	–	/**
1636	–	* Tries to pop and resume a spare thread.
1637	–	* @param updateCount if true, increment running count on success
1638	–	* @return true if successful
1639	–	*/
1640	–	private boolean tryResumeSpare(boolean updateCount) {
1641	–	WaitQueueNode q;
1642	–	while ((q = spareStack) != null) {
1643	–	if (casSpareStack(q, q.next)) {
1644	–	if (updateCount)
1645	–	updateRunningCount(1);
1646	–	q.signal();
1647	–	return true;
1648	–	}
1649	–	}
1650	–	return false;
1651	–	}
1652	–
1653	–	/**
1654	–	* Pops and resumes all spare threads. Same idea as ensureSync.
1655	–	* @return true if any spares released
1656	–	*/
1657	–	private boolean resumeAllSpares() {
1658	–	WaitQueueNode q;
1659	–	while ( (q = spareStack) != null) {
1660	–	if (casSpareStack(q, null)) {
1661	–	do {
1662	–	updateRunningCount(1);
1663	–	q.signal();
1664	–	} while ((q = q.next) != null);
1665	–	return true;
1666	–	}
1667	–	}
1668	–	return false;
1669	–	}
1670	–
1671	–	/**
1672	–	* Pops and shuts down excessive spare threads. Call only while
1673	–	* holding lock. This is not guaranteed to eliminate all excess
1674	–	* threads, only those suspended as spares, which are the ones
1675	–	* unlikely to be needed in the future.
1676	–	*/
1677	–	private void trimSpares() {
1678	–	int surplus = totalCountOf(workerCounts) - parallelism;
1679	–	WaitQueueNode q;
1680	–	while (surplus > 0 && (q = spareStack) != null) {
1681	–	if (casSpareStack(q, null)) {
1682	–	do {
1683	–	updateRunningCount(1);
1684	–	ForkJoinWorkerThread w = q.thread;
1685	–	if (w != null && surplus > 0 &&
1686	–	runningCountOf(workerCounts) > 0 && w.shutdown())
1687	–	--surplus;
1688	–	q.signal();
1689	–	} while ((q = q.next) != null);
1690	–	}
1708		}
1709		}
1710
1711		/**
1712		* Interface for extending managed parallelism for tasks running
1713	<	* in ForkJoinPools. A ManagedBlocker provides two methods.
1714	<	* Method {@code isReleasable} must return true if blocking is not
1715	<	* necessary. Method {@code block} blocks the current thread
1716	<	* if necessary (perhaps internally invoking isReleasable before
1717	<	* actually blocking.).
1713	>	* in {@link ForkJoinPool}s.
1714	>	*
1715	>	* <p>A {@code ManagedBlocker} provides two methods.  Method
1716	>	* {@code isReleasable} must return {@code true} if blocking is
1717	>	* not necessary. Method {@code block} blocks the current thread
1718	>	* if necessary (perhaps internally invoking {@code isReleasable}
1719	>	* before actually blocking). The unusual methods in this API
1720	>	* accommodate synchronizers that may, but don't usually, block
1721	>	* for long periods. Similarly, they allow more efficient internal
1722	>	* handling of cases in which additional workers may be, but
1723	>	* usually are not, needed to ensure sufficient parallelism.
1724	>	* Toward this end, implementations of method {@code isReleasable}
1725	>	* must be amenable to repeated invocation.
1726	>	*
1727		* <p>For example, here is a ManagedBlocker based on a
1728		* ReentrantLock:
1729	<	* <pre>
1730	<	*   class ManagedLocker implements ManagedBlocker {
1731	<	*     final ReentrantLock lock;
1732	<	*     boolean hasLock = false;
1733	<	*     ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1734	<	*     public boolean block() {
1735	<	*        if (!hasLock)
1736	<	*           lock.lock();
1737	<	*        return true;
1738	<	*     }
1739	<	*     public boolean isReleasable() {
1740	<	*        return hasLock || (hasLock = lock.tryLock());
1741	<	*     }
1729	>	*  <pre> {@code
1730	>	* class ManagedLocker implements ManagedBlocker {
1731	>	*   final ReentrantLock lock;
1732	>	*   boolean hasLock = false;
1733	>	*   ManagedLocker(ReentrantLock lock) { this.lock = lock; }
1734	>	*   public boolean block() {
1735	>	*     if (!hasLock)
1736	>	*       lock.lock();
1737	>	*     return true;
1738	>	*   }
1739	>	*   public boolean isReleasable() {
1740	>	*     return hasLock || (hasLock = lock.tryLock());
1741	>	*   }
1742	>	* }}</pre>
1743	>	*
1744	>	* <p>Here is a class that possibly blocks waiting for an
1745	>	* item on a given queue:
1746	>	*  <pre> {@code
1747	>	* class QueueTaker<E> implements ManagedBlocker {
1748	>	*   final BlockingQueue<E> queue;
1749	>	*   volatile E item = null;
1750	>	*   QueueTaker(BlockingQueue<E> q) { this.queue = q; }
1751	>	*   public boolean block() throws InterruptedException {
1752	>	*     if (item == null)
1753	>	*       item = queue.take
1754	>	*     return true;
1755		*   }
1756	<	* </pre>
1756	>	*   public boolean isReleasable() {
1757	>	*     return item != null || (item = queue.poll) != null;
1758	>	*   }
1759	>	*   public E getItem() { // call after pool.managedBlock completes
1760	>	*     return item;
1761	>	*   }
1762	>	* }}</pre>
1763		*/
1764		public static interface ManagedBlocker {
1765		/**
1766		* Possibly blocks the current thread, for example waiting for
1767		* a lock or condition.
1768	<	* @return true if no additional blocking is necessary (i.e.,
1769	<	* if isReleasable would return true)
1768	>	*
1769	>	* @return {@code true} if no additional blocking is necessary
1770	>	* (i.e., if isReleasable would return true)
1771		* @throws InterruptedException if interrupted while waiting
1772	<	* (the method is not required to do so, but is allowed to).
1772	>	* (the method is not required to do so, but is allowed to)
1773		*/
1774		boolean block() throws InterruptedException;
1775
1776		/**
1777	<	* Returns true if blocking is unnecessary.
1777	>	* Returns {@code true} if blocking is unnecessary.
1778		*/
1779		boolean isReleasable();
1780		}
1781
1782		/**
1783		* Blocks in accord with the given blocker.  If the current thread
1784	<	* is a ForkJoinWorkerThread, this method possibly arranges for a
1785	<	* spare thread to be activated if necessary to ensure parallelism
1786	<	* while the current thread is blocked.  If
1787	<	* {@code maintainParallelism} is true and the pool supports
1788	<	* it ({@link #getMaintainsParallelism}), this method attempts to
1789	<	* maintain the pool's nominal parallelism. Otherwise if activates
1790	<	* a thread only if necessary to avoid complete starvation. This
1791	<	* option may be preferable when blockages use timeouts, or are
1792	<	* almost always brief.
1793	<	*
1794	<	* <p> If the caller is not a ForkJoinTask, this method is behaviorally
1795	<	* equivalent to
1796	<	* <pre>
1797	<	*   while (!blocker.isReleasable())
1752	<	*      if (blocker.block())
1753	<	*         return;
1754	<	* </pre>
1755	<	* If the caller is a ForkJoinTask, then the pool may first
1756	<	* be expanded to ensure parallelism, and later adjusted.
1784	>	* is a {@link ForkJoinWorkerThread}, this method possibly
1785	>	* arranges for a spare thread to be activated if necessary to
1786	>	* ensure sufficient parallelism while the current thread is blocked.
1787	>	*
1788	>	* <p>If the caller is not a {@link ForkJoinTask}, this method is
1789	>	* behaviorally equivalent to
1790	>	*  <pre> {@code
1791	>	* while (!blocker.isReleasable())
1792	>	*   if (blocker.block())
1793	>	*     return;
1794	>	* }</pre>
1795	>	*
1796	>	* If the caller is a {@code ForkJoinTask}, then the pool may
1797	>	* first be expanded to ensure parallelism, and later adjusted.
1798		*
1799		* @param blocker the blocker
1759	–	* @param maintainParallelism if true and supported by this pool,
1760	–	* attempt to maintain the pool's nominal parallelism; otherwise
1761	–	* activate a thread only if necessary to avoid complete
1762	–	* starvation.
1800		* @throws InterruptedException if blocker.block did so
1801		*/
1802	<	public static void managedBlock(ManagedBlocker blocker,
1766	<	boolean maintainParallelism)
1802	>	public static void managedBlock(ManagedBlocker blocker)
1803		throws InterruptedException {
1804		Thread t = Thread.currentThread();
1805	<	ForkJoinPool pool = (t instanceof ForkJoinWorkerThread?
1806	<	((ForkJoinWorkerThread)t).pool : null);
1807	<	if (!blocker.isReleasable()) {
1808	<	try {
1809	<	if (pool == null ||
1810	<	!pool.preBlock(blocker, maintainParallelism))
1775	<	awaitBlocker(blocker);
1776	<	} finally {
1777	<	if (pool != null)
1778	<	pool.updateRunningCount(1);
1779	<	}
1805	>	if (t instanceof ForkJoinWorkerThread) {
1806	>	ForkJoinWorkerThread w = (ForkJoinWorkerThread) t;
1807	>	w.pool.awaitBlocker(blocker);
1808	>	}
1809	>	else {
1810	>	do {} while (!blocker.isReleasable() && !blocker.block());
1811		}
1812		}
1813
1814	<	private static void awaitBlocker(ManagedBlocker blocker)
1815	<	throws InterruptedException {
1816	<	do;while (!blocker.isReleasable() && !blocker.block());
1786	<	}
1787	<
1788	<	// AbstractExecutorService overrides
1814	>	// AbstractExecutorService overrides.  These rely on undocumented
1815	>	// fact that ForkJoinTask.adapt returns ForkJoinTasks that also
1816	>	// implement RunnableFuture.
1817
1818		protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
1819	<	return new AdaptedRunnable(runnable, value);
1819	>	return (RunnableFuture<T>) ForkJoinTask.adapt(runnable, value);
1820		}
1821
1822		protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
1823	<	return new AdaptedCallable(callable);
1823	>	return (RunnableFuture<T>) ForkJoinTask.adapt(callable);
1824		}
1825
1826	+	// Unsafe mechanics
1827
1828	<	// Temporary Unsafe mechanics for preliminary release
1829	<	private static Unsafe getUnsafe() throws Throwable {
1828	>	private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1829	>	private static final long workerCountsOffset =
1830	>	objectFieldOffset("workerCounts", ForkJoinPool.class);
1831	>	private static final long runStateOffset =
1832	>	objectFieldOffset("runState", ForkJoinPool.class);
1833	>	private static final long eventCountOffset =
1834	>	objectFieldOffset("eventCount", ForkJoinPool.class);
1835	>	private static final long eventWaitersOffset =
1836	>	objectFieldOffset("eventWaiters",ForkJoinPool.class);
1837	>	private static final long stealCountOffset =
1838	>	objectFieldOffset("stealCount",ForkJoinPool.class);
1839	>	private static final long spareWaitersOffset =
1840	>	objectFieldOffset("spareWaiters",ForkJoinPool.class);
1841	>
1842	>	private static long objectFieldOffset(String field, Class<?> klazz) {
1843	>	try {
1844	>	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1845	>	} catch (NoSuchFieldException e) {
1846	>	// Convert Exception to corresponding Error
1847	>	NoSuchFieldError error = new NoSuchFieldError(field);
1848	>	error.initCause(e);
1849	>	throw error;
1850	>	}
1851	>	}
1852	>
1853	>	/**
1854	>	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1855	>	* Replace with a simple call to Unsafe.getUnsafe when integrating
1856	>	* into a jdk.
1857	>	*
1858	>	* @return a sun.misc.Unsafe
1859	>	*/
1860	>	private static sun.misc.Unsafe getUnsafe() {
1861		try {
1862	<	return Unsafe.getUnsafe();
1862	>	return sun.misc.Unsafe.getUnsafe();
1863		} catch (SecurityException se) {
1864		try {
1865		return java.security.AccessController.doPrivileged
1866	<	(new java.security.PrivilegedExceptionAction<Unsafe>() {
1867	<	public Unsafe run() throws Exception {
1868	<	return getUnsafePrivileged();
1866	>	(new java.security
1867	>	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1868	>	public sun.misc.Unsafe run() throws Exception {
1869	>	java.lang.reflect.Field f = sun.misc
1870	>	.Unsafe.class.getDeclaredField("theUnsafe");
1871	>	f.setAccessible(true);
1872	>	return (sun.misc.Unsafe) f.get(null);
1873		}});
1874		} catch (java.security.PrivilegedActionException e) {
1875	<	throw e.getCause();
1875	>	throw new RuntimeException("Could not initialize intrinsics",
1876	>	e.getCause());
1877		}
1878		}
1879		}
1815	–
1816	–	private static Unsafe getUnsafePrivileged()
1817	–	throws NoSuchFieldException, IllegalAccessException {
1818	–	Field f = Unsafe.class.getDeclaredField("theUnsafe");
1819	–	f.setAccessible(true);
1820	–	return (Unsafe) f.get(null);
1821	–	}
1822	–
1823	–	private static long fieldOffset(String fieldName)
1824	–	throws NoSuchFieldException {
1825	–	return UNSAFE.objectFieldOffset
1826	–	(ForkJoinPool.class.getDeclaredField(fieldName));
1827	–	}
1828	–
1829	–	static final Unsafe UNSAFE;
1830	–	static final long eventCountOffset;
1831	–	static final long workerCountsOffset;
1832	–	static final long runControlOffset;
1833	–	static final long syncStackOffset;
1834	–	static final long spareStackOffset;
1835	–
1836	–	static {
1837	–	try {
1838	–	UNSAFE = getUnsafe();
1839	–	eventCountOffset = fieldOffset("eventCount");
1840	–	workerCountsOffset = fieldOffset("workerCounts");
1841	–	runControlOffset = fieldOffset("runControl");
1842	–	syncStackOffset = fieldOffset("syncStack");
1843	–	spareStackOffset = fieldOffset("spareStack");
1844	–	} catch (Throwable e) {
1845	–	throw new RuntimeException("Could not initialize intrinsics", e);
1846	–	}
1847	–	}
1848	–
1849	–	private boolean casEventCount(long cmp, long val) {
1850	–	return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
1851	–	}
1852	–	private boolean casWorkerCounts(int cmp, int val) {
1853	–	return UNSAFE.compareAndSwapInt(this, workerCountsOffset, cmp, val);
1854	–	}
1855	–	private boolean casRunControl(int cmp, int val) {
1856	–	return UNSAFE.compareAndSwapInt(this, runControlOffset, cmp, val);
1857	–	}
1858	–	private boolean casSpareStack(WaitQueueNode cmp, WaitQueueNode val) {
1859	–	return UNSAFE.compareAndSwapObject(this, spareStackOffset, cmp, val);
1860	–	}
1861	–	private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1862	–	return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1863	–	}
1880		}

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